You have ebay listed several times. You should include Amazon, I buy most of my stuff from the .ca site! Also include B&H, they ship to the UK and will list UK prices if you use a drop down box.
http://www.hdewcameras.co.uk/ - if you don`t mind grey imports at times with their own UK based warranty repairs
Here is another retailer who gets the thumbs up from me.http://www.jackthehat.co.uk/Just bought an off cam flash cord from them. Cheapest I could find and good delivery.I asked around elswhere before I made my purchase and they got positve remarks from my contacts
Ian Kerr runs http://www.flashcamera.co.uk/ - very good prices and service.
Should have added this link to my other post about the new battery grip.Anyways, I have used these a few times for buying gear and they been fine.http://www.mpbphotographic.co.uk/THey will also buy your gear if you want to sell, but the last time I offered them some stuff the prices they quoted were not great. You can also part exchange.