It's less about being 'white' in the UK than being 'English' hence why Brits often get very annoyed when people say 'the Queen of England' and 'you live in England right' when talking to Brits. The UK is made up a few countries, Scotland, Wales, Northern Ireland, Isle of Man, Channel Islands and Cornwall with the Shetland Islands coming in later. Each of these feels to some extent or other subjugated by the English who have at some time invaded their countries. Languages were forbidden, people moved ( the Highland Clearances and the Irish Potato Famine for example). Everything was ruled from London and everyone who was not English was quite simply inferior . The Englishman ( not women though!) was the perfect white man who was the superior to all others. He had a duty to bring civilisation to the natives ( this included the Scots, Irish and Welsh of course) and would behave like a benevolent dictator. This was fostered and still is actually by the public school system ( Public schools of course being the very expensive private schools) so like our class system, where saying the middle class needs more help would bring derision from all sides, the perception of colour is somewhat different from how it is in the USA. We've had black people here since the Romans.
Britain's first black community in Elizabethan London - BBC News.
Having colonies which were regarded as paternalistic made British people used to all sorts of creeds and colours, didn't mean there wasn't prejudice of course but we've never had slavery on home soil ( what went on 'out there' was often ignored until the great abolitionists started campaigning) so black people have never been regarded in the same way as they can be in the USA.
While we have the nasty groups like UKIP, BNP and EDL who are neo Nazis ( yes that UKIP with the Nazi Nigel Farage) and hate just about everyone, stirring up hatred for Muslims in particular at the moment ( it doesn't matter how much you tell them Muslim isn't a race, they continue to believe it), race isn't such an issue here as it is in the USA. By the way to us and Europeans, in fact the rest of the world you are all just Americans whatever you call yourselves, sometimes it's 'bloody Yanks' lol but you are all just Americans to us and we don't use word like 'Black British' or 'Asian British' in the same way as you seem to differentiate. So for us basically, being British ( or English lol) is the important thing not the colour as much. Everyone else is 'them'.
'Them' is the important difference not colour, Jews, Celts, Irishmen et al are 'them' not 'us'. We use words to find out whether they are them or us, that's why English is such a minefield here. what words you use define what you are. A black person who uses the right words is 'us' a Scotsman who doesn't is 'them'. Take for example meals... what do you call the meal taken in the middle of the day and then in the evening? that is quite likely to define your place in our society! Here too your class is still the important thing whatever Thatcher thought, it is still simply divided on class, money will never make you anything other than rich.
Life here I suppose is complicated for non Brits, many books have been written about the class system, the cultural divide and the way we live. some complain here how immigrants don't assimilate but it's hard not to blame them when we have so many unspoken rules about your place in society. This isn't a political comment by the way but it is noticeable when we have a public school educated Prime Minister and government such as Cameron's how things regress back into Victorian ideas of paternalism and how they 'know best' lol. Have a look at Boris Johnson our Foreign Minster's manner with the 'natives' (yep that's Americans too lol). His comments aren't meant in a racist way he just opens his mouth and out trot all the old colonial bonhomie platitudes visiting bigwigs used to come with to pat the natives on the back with. Then everyone cringes and his aides have to back pedal and spin what he's said. His ilk is why everyone non English hates the English and prefers just about anyone else from anywhere in the world.