Someone I knew went for an interview as head of maths in a London school. He was very well qualified. They did not appoint so he rang up to enquire why he was unsuitable. His Welsh accent apparently. This was in the 1990s.
So yes, I agree, white UK citizens can experience racism.
I also agree with Bags that a black immigrant to Uk might not experience racism. Depends on what they are doing, where they are doing it and who they are interacting with. A woman I know who is an independent consultant was saying the other day that being african in appearance was actually an advantage at times in her business, because she gets noticed (much more than white men in suits) and people always remember her.
I did know someone who once went on a demo in Oxford against a hairdresser who refused to cut "black" hair - but that was about 45 years ago.
Army horses loose on London streets