this is bbc world news the headlines. iran has hoisted its flag on the masthead of a british oil tanker it seized in the straits of hormuz. but despite the move, tehran says "prudence and foresight" are required to defuse tension between the two countries. riot police have fired tear gas and rubber bullets at protesters in hong kong following another pro—democracy rally. officers charged demonstrators who refused to disperse. the protests began over a controversial extradition bill.. exit polls in ukraine suggest that president volodymyr zelensky‘s party will win the largest number of seats in parliament, with an estimated 44% of the votes.

but that's short of an overall majority. the british finance minister philip hammond says he'll resign if boris johnson becomes prime minister. he said he can't accept mrjohnson‘s promise to take britain out of the eu at the end of october — deal or no deal. at ten o'clock, ben brown will have the news, but first, it is our world. safa and marwa are identical twins joined at the head. their family, from pakistan, want doctors to separate them. great ormond street in london is one of the few hospitals in the world with the expertise to do it. this is safa's brain, that's marwa's brain. what we need to achieve is effectively untwist the brains, and that is difficult, pretty difficult to do just in your head.

but it is perilous. the bbc was given unique access to chart the complex medical and ethical choices made... this is the day, the moment of truth, and everything hasjust got to be perfect. ..in the hope of giving the girls independent lives. safa and marwa are 21 months old, and were born in pakistan. they have come to london's great ormond street hospital with their mother zainab, grandfather and uncle, and are under the care of neurosurgeon owasejeelani. it is clearly very difficult to go through life when you are joined together like that, so it does make a very persuasive case in favour of doing the surgery. the family are very clear on that.

clearly, life being separate is very much better than life together. if we felt there was not a very, very high chance that we could do it safely, we would be thinking about whether we should do it or not. i think the whole team feel that there is an excellent chance of a successful separation here. the twins' father died just before they were born, and then it took more than a year of fundraising before a donor stepped in to cover the medical costs. safa and marwa are what's known as craniopagus twins, which meansjoined at the head. their skull is one long tube. the twins share many key blood vessels.

separating these will be a major challenge. both twins' brains have a distorted appearance. one half is pointing up into the other girl's skull cavity. every last detail of the twins' extraordinary anatomy has been recreated digitally. plastic surgeon david dunaway will be in charge of rebuilding the girls‘ skulls after neurosurgeon owasejeelani has separated the twins' brains. they showed me how sd modelling has helped them to prepare. this hemisphere, which is the right hemisphere of the brain, is standing up, so this is actually projecting into the other child's skull. what we need to achieve is to effectively untwist the brains, and that's difficult, pretty difficult to do just in your head. for surgeons it is massively helpful, actually being able to touch and hold things makes so much difference to understanding

how things are. we spent a long time looking at these models and going through the what—ifs. numerous models of the twins' brains and shared skull had been created using this 3d printer. the whole process takes two days. this one will help surgeons plan how best to divide the layer of skin on the girls‘ skull once they are separated. and they're not only using physical models. this is surgery without scalpels. absolutely incredible. this is exactly what we wanted. virtual reality has helped the team plan how to divide the twins' shared arteries and veins. it works, it really works. and so now we can see a whole lot more information, a level of detail we've not been able to access previously.

this is clearly the way of the future. we're using this technology for a highly complex case, but many other routine operations that we do, brain tumours, blood malformations, so on and so forth, the rest of those malformations, this would be hugely, hugely beneficial for those cases as well. ok, have we got everyone here? yeah? so we have one case for the list today, safa and marwa, two kids, one case. the surgery is so complex it will happen in three stages over several months. and the twins won't be physically separate until the final operation.

the aim of the first operation is to separate the twins' shared arteries. at present, each child is supplying the other‘s brain with blood. one, two, and three. what we're doing now is, the two arteries that are going from one twin to the other, so we can see the artery but to do anything to it we'll use the microscope. so the artery from safa going to supply marwa's brain has been clamped. but every time this is done, there's a risk of brain damage.

ok, so the brain's looking good. the twins have been in theatre now for more than seven hours. and there are still several hours of this operation to go. so far, everything is going to plan, and both girls are doing well. while one team works on the twins, another, led by david dunaway, constructs a frame made from pieces of the girls‘ skull which can be detached in subsequent operations. this central segment will be our rigid keel to hold the head together. what we need to do is make sure that the twins are rigidly together. being older, they‘re pretty active, and so whatever we do really has to be strong enough to resist the twisting and bending forces that they‘ll be putting on their heads. the first operation lasts 15 hours.

zainab has seven more children back in pakistan, aged 5—16. all of them were born at home, but with this pregnancy she was advised to deliver in hospital. it was not until five days after delivery by caesarean section that zainab was introduced to her daughters, initially by photo. zainab says the twins have distinct personalities.

after a month, the twins are back in theatre. this is safa‘s brain, it looks happy... this time the surgeons will separate the shared network of veins that drain blood from twin‘s brain. but disturbing this equilibrium could also do permanent damage. a portion of each twin‘s brain is being supplied by the other twin. so there is a real risk of causing a stroke at the time of the surgery, that is something that is weighing heavily on us. there could be something down there that i can‘t see at the moment. the more the surgeons try to divide the vessels that link and nourish them, the more unstable

the twins become. we're going to have to take ventilation down. 0k? down? marwa‘s heart begins to fail. we are not stable, but we are less unstable. good enough for me. the anaesthetists manage to stabilise the girls so the operation can continue. because marwa is clearly the weaker twin, the surgeons decide to give her a key shared vein. the operation lasts 20 hours. so i‘m relieved, i‘m relieved. i mean, there was a chance we were going to... potentially lose marwa during the surgery. it‘s been a big operation,

but hopefully if they wake up as we hope they will, it‘s gone well. yeah. but shortly after surgery, safa suffers a stroke. there was a period on tuesday evening where...we felt that we were very close to losing safa, and that she stayed in that critical state for... ..for 48—72 hours after the surgery. it was a very difficult time for the girls, their families and the entire team looking after them.

in a break from their work at great ormond street, the two lead surgeons are in ireland to meet another set of twins. it‘s eight years since they last saw ritaj and rital. it‘s hard to believe that these sisters, born in sudan, were once joined at the head. thank you! you are very welcome. back then the surgeons feared the girls might die unless separated. and this was rital and ritaj just one month after surgery. each parent able to hold a child in their arms. i hope that they will get a normal life and be treated as normal human beings. their father is now a doctor in ireland. we are now sitting here with two healthy twins, just like what i hoped at that time. so it‘s a great moment

in my life as well. so the dream came true? exactly, yeah. i‘m a very proud dad now. that was a very hard time. and at the same time it was a happy time because of the conclusion. rital has some learning difficulties. by the long—term outcome of the twins‘ separation has been hailed as a major success. the surgeons believe it‘s because it was done in the first year of life. what we put the two kids through and the brains through is a lot. and the younger brains and the younger circulations are better adapted. everything is easier. a one—year—old's regenerative capacities are so much better. the skin heals better, it stretches better, the bone grows in better.

they‘re setting up a charity so that funds are available to pay for early intervention in future cases and for research into the best way to separate conjoined twins. it‘s january 2019. i think the last two months after their last operation on the brain has been a little bit of a stormy time for safa and marwa. they‘ve had ups and downs with infections and temperatures and marwa‘s heart is having work quite hard for both of them and that‘s causing her a few challenges. but they‘re hanging in there. and they‘re both reasonably well. the next challenge for the surgeons is to ensure each twin will have enough skin to cover their skull when they‘re eventually separated. they do this by encouraging the skin to expand.

the tissue expanders are balloons that sit underneath the skin and they have a tiny little port attached to them through which we can inject saline. so the idea now is that we will gradually inject the tissue expanders and they will blow up like a balloon and the skin over the top of them will stretch. and it‘s a very, very effective technique of making more skin out of the skin we have available so that when we come to separate safa and marwa there‘s enough skin to cover both of their heads. these rare cases leave a lasting impact on the surgeons. if i may, i haven‘t asked david‘s permission to say this. but the last separation that we did, when the kids were finally separated, and everyone was overjoyed and so on and so forth, and people were happy, and i looked at david and he had tears in his eyes. and he denies it to this day, but he did at that time. yeah. ithink...

everybody has been so invested in this for so long. it is a surprisingly emotional thing, i think, when they finally come apart. and when that experience of them actually leaving the operating theatre as two separate people is quite indescribable. at last, four months since the first surgery, the day of separation. two forceps. all laid out. so this is safa‘s brain that‘s marwa‘s brain. if you do, give me a seven. little by little, the bone and the tissue which joins them is cut.

so they are separate apart from that piece ofjewellery. and then, after seven hours, the final connection is severed. fantastic. 0k. done. it's in a very emotional moment. we've been working a long time to get them here. they've been through so many operations and now it's worked. yeah, we have to put them together now. so we've taken them apart and now we have to reconstruct their heads. marwa is still in the operating theatre through here, while safa has been moved just next door.

for the first time, the survival of each of the twins is not dependent on the other. and that‘ll make it easier for the two surgical teams to regulate their heart rate, blood pressure, and other vital signs. safa and marwa‘s brains used to have a distorted shape. but four months ago a plastic sheet was inserted between them and by gradually tightening the pressure it has largely corrected their appearance, essential before their skulls can be rebuilt. this means both teams can begin reconstruction. the patchwork of skull pieces are shared between theatres. so a piece for me, a piece for you. to have enough to cover their heads, each fragment must be divided in two. the skull is very usefully designed in three layers. so there is an inner layer of very thick, tough bone, an outer layer of thick,

tough bone, and in between it the bone is like a honeycomb, so you can split the bone, it‘s half the thickness, but it means we should be able to cover nearly all of the head with bone afterwards. this shows the jigsaw of bone fragments that were pieced together to form the skull of marwa on the left and safa on the right. the gaps have been seeded with bone cells. and in the months to come these should slowly close up. the final task of the 17—hour operation is to stretch the skin over their reconstructed skulls. it‘s a pretty amazing day, isn‘t it? everything is good.

thank you. oh, what a day. they have been quite amazing throughout, actually. they‘re a great family and i think they draw strength from one another. and they seem to be getting through it very well. we asked mum who she would pick up first, whether it was safa or marwa? and the answer was both — with support! so, ah, yeah... the road to recovery for the twins is slow, but four months after separation, safa and marwa are beginning to make progress. # hello, safa. # hello, marwa. # how are you today? the twins have daily physiotherapy. it‘s hoped this will help them reach some basic milestones —

learning to roll, sit, and hold their heads up. # twinkle, twinkle, little star. # how i wonder what you are... safa has not fully recovered from her stroke. we made the decision that the bulk of the common vessels go to marwa, the weaker twin. and because of the decision, safa suffered a stroke. so what i really want to see is the weakness safa has at the moment, and she has a weakness in her left arm and left leg, improves. so for me the big moment‘s going to be when she walks and when she uses her left arm properly. because, you know, i have given her that weakness and for me that‘s a hard thing. nearly a year since they were admitted to hospital, the girls are leaving

great ormond street. the family will stay in london until the twins are strong enough to return to pakistan. the donor who paid for the surgery is continuing to support them. they are clearly going to face some challenges. but i think, overall, it‘s a positive outcome for them. they are going to need support, but they have a chance of leading a happy life. whatever hurdles safa and marwa may face in years to come, they will at least do that as a separate, independent girls. twins still, but conjoined no more.

hello. we‘ve got some big changes in our weather coming up over the next few days. for england and wales it‘s mainly going to be a hot and sunny week ahead, with surging temperatures. scotland and northern ireland becoming warm or very warm for a time, but there‘s the risk of some thundery downpours developing here as well. now, towards the middle part of the week, we‘ll have south—easterly winds bringing the hot air in from europe. temperatures in the uk could reach around 3a celsius, so some of the hottest weather of the year, and in paris potentially into the 40s. if that happens, we could set a new temperature record for the french capital, so we‘ll be keeping a close eye on developments in france as well over the next few days.

in recent hours we‘ve been keeping an eye on this stripe of cloud that stretches well into the atlantic, and this is a wiggling, waving weather front. it‘s bringing some heavy rain to the north—west of the uk. now, increasingly, as we head on through monday, the rain will become focused across western parts of scotland, where there isa risk of some localised flooding. south—westerly winds elsewhere, and after a rather cloudy start to the day, that cloud will thin and melt away with increasingly sunny skies through the afternoon. it becomes warm as well, temperatures 25 degrees in belfast, 2a for aberdeen, mid 20s widely in wales, but across eastern england we should see temperatures up to 29 degrees, so a big increase in temperatures compared with what we‘ve seen over the weekend. by tuesday, the winds turn more to a south—easterly, dragging that hot air from europe. the vast majority of the uk having dry weather. and it‘s going to be very warm, if not hot. 27 in aberdeen, mid—20s for western counties of northern ireland. into the 30s for england and wales.

and probably 33, 3a degrees in the east. after such a hot day overnight, those temperatures slow to fall. these are the temperatures at ten o‘clock at night, still up at 27 in london and there‘ll be some thunderstorms breaking out through tuesday night. those storms then push north as we head into wednesday, with some torrential downpours. there is a risk of some localised flash flooding from the heaviest of these storms. the winds start to turn more to a south—westerly direction and the humidity will come down just a little bit on wednesday, but it stays hot, particularly across eastern england. temperatures still into the low 30s here. the winds again turn more to a south—east on thursday, so we‘ll get more of that hot sunshine being brought in from the near continent, but at the same time, thundery rain starts to develop and northern ireland for western scotland and maybe into wales later in the day as well. with that, we‘ve got some fresh air coming in of the atlantic in the north—west, but it stays hot across eastern england. again highs of around 33, 3a degrees. real changeover takes place on friday, as the atlantic winds begin to have more

of an influence on wales, western england, scotland and northern ireland. so temperatures coming down here still pretty warm across eastern areas of england, and there‘s still a risk of a few thundery showers developing in one or two spots. beyond that, we‘ll look at the weather picture into the weekend and we‘ll take a look at the jet stream pattern. well, instead of having a ridge over us we have more of a trough feature, but the trough is for the west of the uk, that‘s where pressures will tend to develop. by the time they move towards the uk, those low—pressure systems will be quite old. what does that all mean? into the weekend it looks like it will be mainly cloudy with showers. temperatures for many of us returning to near—normal. there will be some sunshine around, and perhaps staying on the warm side toward south—east england. temperatures here still could reach the mid—20s. but, nevertheless, for england and wales in particular, a hot week ahead.

the chancellor philip hammond says he‘ll resign if borisjohnson becomes prime minister. mr hammond says he couldn‘t support a leader who‘s prepared to see a no—deal brexit. it‘s very important that a prime minister is able to have a chancellor who is closely aligned with him, in terms of policy, and i therefore intend to resign to theresa may, before she goes to the palace to tender her own resignation on wednesday. we‘ll have the latest from westminster ahead of a pivotal week in british politics. also tonight... please confirm you are not intending to violate international law. a recording of the moment a royal navy warship tried to stop iran seizing a british tanker. violence erupts again in hong kong, as police use tear gas and rubber