I think the Mile M.52 would have had a great chance, but the British mysteriously cancelled the program when the airframe was all but completed, and handed the research over to the USA. It must have been politics ... there is no other rational explanation.
The story I have seen (a few times) is that the man responsible for the Miles project at the Ministry of War (as it then was) Sir Ben Lockspeiser was horrified at the possibility that this dangerous project was likely to kill a number of young British men just after the horrendous blood-letting of WW2.
I have looked him up he was a veteran of WW1 so I don't think that mentality can be completely discounted.
Geoffrey de Havilland, Jr's death was around this time quite a shock (and reinforcing the 'highly dangerous' and maybe the 'can't be done' reputation of the barrier)
If we also factor in the dire financial situation Britain was in post-war and I can see why such a promising project was canned, however damaging or short-sighted the decision.
Interestingly the (30%) scale model powered by a small rocket went to close to mach 1.4.
As for the Miles people sharing data with Bell?
Well it was supposed to be a reciprocal arrangement from what I've read we showed ours but Bell never did show their research.
(wiki does mention Sir Ben Lockspeiser was known to have an interest in communism after the war - but there is no suggestion he acted to stop the Miles project on behalf of foreign agents etc etc)
As for the Me 262, vanir GregP are right.
The swept wing on the Me 262 was a fortunate accident, it was done for a C0G change; the benefits delaying transonic shock etc were recognised later.
Fundamentally the wing just isn't strong enough (and I am sure I've seen somewhere that it isn't of the right aerofoil section either).
I am certain that I've read that post-war tests in the UK USA proved that before mach 0.9 is reached the aircraft went totally out of control with all control surfaces becoming ineffective.