Undoubtedly the UK needs some YC-like schemes.
The YC FAQ does say “There already is a Y Combinator in your town: Y Combinator. The seed funding business is national, not regional.” and we know that in fact it is international as UK teams have taken part. In fact as far as I know, all the YC-like schemes will consider international applicants.
However, as jlees says, that does not benefit the UK. I believe that a lot of it is to do with national culture differences - the US just has a much stronger ethos of innovation and investment. People are just more likely to be entrepreneurial in the US. Entrepreneurs built America and it’s been part of their culture since colonists first settled there.
Meanwhile, in the UK, most individuals with large amounts of money (enough for angel investing) are either “old money” or have gained their money through conventional high-paying jobs (lawyers, investment bankers) where entrepreneurship is not part of the job per se. Those that do try angel investing, just don’t quite “get it”. Technology is completely alien to some farmer with 100,000 acres who happens to have a spare £100,000, meanwhile biotech investments (my current sector) will scare the bejesus out of most sane angels.
I would love to start a UK YC equivalent, but I would not want to do it without having experienced considerable success through starting and exiting some companies, or through gaining significant experience through VC work (which is closer to my current job). If anything, these experiences are needed just to build the network which we know is more important than the money in these programmes.
As has been mentioned, there are some schemes around in the UK, but there is nothing that /really/ fills YC’s concept-PoC niche. There will be eventually though - once I have got a spare £100 M from successfully selling a few companies I will gladly start one!