this is bbc news. i'm clive myrie. the headlines at 11pm: president trump has signed an order to build a wall on the us border with mexico, one of his main of his main campaign promises. construction could begin in months. nation without borders is not a nation. beginning today, the united states of america gets back control of its borders, gets back its borders. mps will get a chance to scrutinise the government's brexit strategy after theresa may said she'll produce a white paper. the royal bank of scotland is to set aside another $4 billion to pay fines for miss—selling. british scientists have identified 1a new disorders affecting children after analysing the genes of thousands of children with rare, undiagnosed conditions. and on newsnight we find out what the mexicans think about donald trump's proposed border wall and

speak to the playwright david pair about his film on holocaust denial. good evening and welcome to bbc news. president trump has signed an executive order to build a wall along the us border with mexico. it was one of his key pledges during the election campaign. mr trump said he expected construction to start within months and that planning will begin immediately. he insisted that while american taxpayers would have to pay for the initial work, he would expect mexico to reimburse the cost. mexican president enrique pena nieto is reportedly considering cancelling next week's visit to washington following donald trump's order. our correspondent james cook reports from the us—mexico border. donald trump's signature pledge is now one step closer to reality. with a stroke of his pen, the new president ordered

the construction of a great wall on the mexican border. it would begin, he said, within months. a nation without borders is not a nation. beginning today, the united states of america gets back control of its borders. we're going to get the bad ones out. the criminals and the drug deals and gangs and gang members and cartel leaders. the day is over when they can stay in our country and wreak havoc. strengthening and extending the existing barrier on this frontier will be hugely expensive. mr trump has always insisted that mexico will pay, but mexico say it won't and the president now admits american taxpayers will have to cough up first. ultimately, it will come out of what's happening with mexico. we're going to be starting those negotiations relatively soon and we will be in a form reimbursed by mexico. so they'll pay us back? yes.

absolutely. 100%. so the american taxpayer will pay for the wall at first? all it is, is we'll be reimbursed at a later date. but here in a mexican border city, business leaders are worried about the impact on trade and sceptical about the president's plans. the problem is that the majority of americans are not really familiar with the border and, consequently the idea of a wall seems to be appealing. we already have one. we call it the tortilla curtain, but the truth of the matter is that, you know, i think that's a symbol. this fence at the pacific ocean is the very start of the land border between mexico and the united states and president trump has always said he wants to build a much taller, a much better, much bigger wall, stretching all the way from here, nearly 2,000 miles to texas. # this land is your land.

# this land is my land... but even in liberal california there's backing for president trump's hard line on immigration, not least from these supporters who call themselves the trumpettes. i think it's a good thing. you know, i always say my scripture is, "i sought for a man who build a wall." i was reading that the other day and it just stuck out in my spirit because we need protection, and i pray for america and i pray that god will shore up the border of our nation. as well as the wall, president trump is promising to deport immigrants who commit crimes, to cut funding to states like california which refuse to arrest most illegal aliens and to hire 10,000 more enforcement agents. his actions are bold, sweeping and intensely divisive. james cook, bbc news, on the us—mexico border. the prime minister has decided she is prepared to publish a more detailed government paper on the strategy for brexit.

theresa may said she recognised there was an appetite for a white paper after a number of conservative mstoined labour in asking for a paper to be published. the supreme court ruled yesterday that mrs may could not begin the brexit process without pa rliament‘s approval. 0ur deputy political editor john pienaar reports. remember him in the goggles? a once dominant pm out on his ear when britain chose brexit. what happens next? david cameron's doing charity work now, today visiting a medical research lab. reporter: are you worried about defeat prime minister? now, his successor‘s got her hands full with the tactical battle for brexit. and today, theresa may kept a half step ahead of her critics. she'd outlined her brexit game plan in a big speech, they wanted it in black and white. and as the time came for questions... ..a concession. she'd held off promising mps a policy paper, but now... i can confirm to the house that our plan will be set

out in a white paper, published in this house. jeremy corbyn was caught on the hop. could we know when this white paper is going to be available to us? but he ploughed on. will they withdraw the threats to destroy the social structure of this country by turning us into the bargain basement she clearly threatens? but the prime minister's kept the initiative and the brexit paper is unlikely to tell mps more than they know now. it was an easy concession for theresa may to make, but tory mps worried about brexit welcomed it. she's also keen to appear ahead of the game when she visits donald trump in the white house later this week. and she told mps she won't duck policy differences. i am not afraid to speak frankly to a president of the united states. i'm able to do that because we have that special relationship. mps queued to offer issues where she could take on the new president. he must abide by and not withdraw from the paris climate change treaty.

president trump has repeatedly said that he will bring back torture as an instrument of policy. when she sees him on friday, will the prime minister make clear that in no circumstances will she permit britain to be dragged into facilitating that torture? will the prime minister tell president trump that she is not prepared to lower our food and safety standards or to open health systems for privatisation? her answer, she and her government would stand their ground. we will put uk interests and uk values first. another former prime minister's been in brussels, tony blair knows getting close to the white house at the wrong time can end badly. mps on all sides are anxious theresa may remembers that lesson. john pienaar, bbc news, westminster. the royal bank of scotland, which is mostly owned by the taxpayer, is to set aside another $4 billion to pay fines for mis—selling.

royal bank of scotland is in the middle of a restructuring, which includes asset sales, job cuts and multi—billion dollar charges to settle litigation and pay regulatory fines for past misconduct. british scientists have identified 14 new disorders affecting children after analysing the genes of thousands of children with rare, undiagnosed conditions. identifying the genes responsible should lead to a greater understanding of the serious disorders which affect the development of the brain and body and might eventually lead to treatments. 0ur medical correspondent fergus walsh has the story. caitlin, so nice to meet you. a big moment for these two families, meeting for the first time. ten—year—old tamika and nine—year—old caitlin have the same newly identified genetic condition, called cdk 13 disorder. there are only 11 known cases in the uk. the girls are so alike, they could be sisters. living so close, we could have easily bumped into each other. do you think we would have gone home with the wrong child? looking at them, it would have been

easy, they are so similar. it's quite amazing to finally come across somebody who also has a child so different to anybody else‘s child and yet, here we are, and they are like twins. they are. to look at them, they are so similar, aren't they? the developmental disorder affects the girls' learning and communication. why do you think you took the wrong child? tamika has good language skills, caitlin has only a few words. it gives me hope as well, seeing tamika talking so much. it definitely gives me hope that caitlyn‘s speech will form. this is where caitlin and tamika's genetic condition was identified, at the wellcome trust sanger institute, near cambridge. they mapped their genes and found an identicalfault in their dna, but the mutation was not passed on by their parents, so how is that possible? each of us inherits half our dna

from our mother, through the egg and our father in the sperm. sometimes, when those genes are passed on, spontaneous mutations occur that cause rare developmental disorders in children. the older the parents, the more likely that is to happen. scientists here have identified 14 new developmental disorders and calculated that one in every 300 babies will be affected by a spontaneous genetic condition, not carried in their parents' dna. in the uk, that amounts to around 2,000 children every year. the research, in the journal nature, provides reassurance for many families all over the country. the discoveries end the long odyssey that these parents have had trying to find the underlying cause of their child's condition. it provides them with the risk for future pregnancies. which, for these conditions,

is actually very low. and it provides opportunities for research into the causes and possible therapies that might be applied. katya was told last year that she had not passed on tamika's genetic condition and that gave her confidence to have another child, timo, who's unaffected. both families say being part of this research has been hugely rewarding. it's like belonging to a club or a new—found family. yes. it has felt like we've been, for the whole nine years, that we've just been on our own, that there's been no one else out there. but now, knowing that there are other families. all changed? yes, completely. yeah. fergus walsh, bbc news. a brief look at some of the day's other other news stories: more than 4,000 people have been sleeping rough every night on england's streets. the latest figures show that while london has the highest number of homeless people, more than half of councils in england recorded a rise in rough sleepers, compared to the previous year.

northumbria university has apologised and been fined £a00,000 after two people nearly died taking part in a science experiment. the students were accidentally given enough caffeine for 300 cups of coffee, 100 times the intended dose. one of american television's best—loved stars mary tyler moore has died at the age of 80. he's probably sitting out there right now thinking that i'm... boy andi right now thinking that i'm... boy and i don't blame him. look what i did! ooohhhhh... in the 1960s, the mary tyler moore show was among the biggest programmes on us television. she also had some success in films, with an oscar nomination for ordinary people. she'd been seriously ill for two years and her representative said she died in the company of family and friends. that's a summary of the news, newsday is coming up at midnight. now on bbc news it's

time for newsnight. the secretary of homeland security, working with myself and my staff, will begin immediate construction of a border wall. applause donald trump paves the way to drastically reduce america's involvement in the united nations, as he signs off on his giant border wall with mexico. what signals is the president sending out about fortress america? i'll ask the former mexican ambassador to the us. also tonight, britain promised hong kong it would help preserve its political freedoms in law. we fear the midnight knock at our door. we are no longer even safe in our own beds. we may be in hong kong, we may have broken no hong kong law, but we can still be made to disappearfrom hong kong soil. nearly 20 years on from the handover to china, democracy looks increasingly fragile. have we let down the people of that former territory? we speak to hong kong's last governor, chris patten. and this:

it puzzles me that you think yourself qualified to attack me, given that i have 30 years experience in the archives and my books have been published by some of the greatest publishing houses in the world. a new film — denial — tells us how holocaust denier david irvine tried to sue a historian in the high court. i ask the scriptwriter david hare about lies and libel in the current climate. good evening. as ever, it started with a tweet. shortly after 2:30am, president trump alerted the world that it was a big day for national security and that he was going to build a wall. the wall — one of the most memorable pledges of his campaign trail — will be constructed along the border with mexico, aimed at fulfilling his pledge to crack down on both illegal immigration and the flow of illegal drugs. the efficiency — possibility even — of a 2,000—mile barrier has raised eyebrows

and is hotly debated, even within trump's own cabinet. his homeland security advisor — retired generaljohn kelly — said it could only be effective to the extent it was backed up by far more sweeping measures, including more manpower and good relations with those south of the border. it'll cost up to £20 billion — money trump insists will be reimbursed by mexico. how unique is this attempt at a fortress? david grossman reports. donald trump continues to lay the foundation stones of his presidency, signing executive orders on issues like rolling back 0bamacare, a freeze on government hiring and withdrawing from trade deals. today he signed an order to deliver perhaps his most famous campaign pledge. we will build a great wall along the southern border. and mexico will pay for the wall. 100%.