With the release of the new 600D the 500D and 550D are starting to come down.
Regular price: 499.98
6% Discount - 6CAMERA = 29.99
After 8% Quidco, it comes out at 432.38.
15.1 megapixel CMOS sensor
Full HD 1080p movie recording with HDMI output for connection to HDTV
ISO range up to 12800
3.4 frames per second continuous shooting mode
Wide-area, nine-point, auto focus system with cross-type central AF point
External Size 21 x 20 x 12 cm
Interior Size 17 x 10 x 16 cm
Note that I personally expect there to be better deals around in the coming months, but if you need/want it now, this is the best price I've seen. For Quidco you have to get Home Delivery, which is free for the 3-5 business day delivery.
One bonus about Best Buy is that they price match to Currys/PC World, Dixons, Comet web prices or any brick and mortar store w/in 10 miles of one of theirs. Jessops *should* be included in that, as there is one w/in 10 miles of the Southampton Best Buy, though you might have to show that you would be willing/able to travel to that store.