our guestsjoining me tonight are george eaton, the political editor of the new statesman, and the chief and former political strategist for the conservative party, jo tanner. the prince of wales says he will keep his views on controversial issues to himself when he becomes king. in a bbc documentary to mark his 70th birthday being broadcast tonight, he says he recognises being heir to the throne and head of state are two different roles. in the past, the prince has campaigned strongly on issues such as the environment and architecture, sometimes accused of "meddling". our royal correspondent nicholas witchell reports. a warning, his report does contain flash photography. charles in nigeria yesterday. a few days from his 70th birthday, representing britain and trying his hand at a little pidgin english. all i can say is that "god don butter my bread." laughter for nearly half a century now, charles has tried, as he puts it, to make a difference for the better. as prince of wales, he has campaigned on the environment, the inner cities, youth opportunities, architecture, to name just four