360 is much cheaper than the PS3 in UK. 360 launched 16 months before the PS3 in the UK. 17 months advantage is a big lead in regards to gaining install base and market exposure and more time for marketing and advertising in the region.
360 has had wo more extra Xmas periods than the PS3 in the UK.
Microsoft puts more time, effort and $$$ into advertising and marketing the 360 in the UK.