A couple of others....
Good old GAP start at a size 0 (which is a UK2-4 I think) and go up from there. Personally their throusers have never fitted but for the top half and skirts, they're second to none. Try their website www.gap.com, and there's so many stores in the UK everyone has a local one!
Also, look for continental clothing brand where the sizes run small. For example, Zara are hell on earth for anyone over a size 14 (which is an XL), and their size small might fit you. There's also Mango, Morgan (as kaztuz recommended) and Moschino (though they can be pricy). Try a google search on Spanish or Italian clothing companies.
Failing that, there's always ebay.... I often find brand new clothes on there for a fraction of the RRP, often designer ones as well.
Good luck x