I just received my first order from
http://equilter.com and am very pleased. Each of the sites we've shared often have something that the others do not, so I find it's a very great idea to look through all of them when you have a specific project in mind.
joflo, I'm not sure about brick and mortar shops but there are probably several online shops based in the UK from which it may be less expensive for you to have items shipped.
http://www.creative-fabrics.co.uk and
http://www.u-handbag.com (a handbag supplies store that also has some fabric selections) are two I know of.