Britain is one of the parts of the UK - the others being Northern Ireland, the channel islands and Gibraltar.
the UK has 5% Muslims - about 2.8 million
the USA has 1.1% Muslims - about 3.5 million
Just to clarify....
England is 5% Muslim, not the UK.
About half of them live in metropolitan London.
Also, because of the British Empire, and because of Europe's proximity to North Africa and the Middle East, England has been accepting Muslim immigrants since the 19th Century.