Hey, by external memory, do you mean an external Hard disk to connect via USB. Personally I can never beat ebuyer. The thing with the larger disks (+1TB) they probably won't be able to run off USB power alone and will need a caddy of some sort.
As for your original question,I think there is still a computer fair running at Bracknell leisure centre quite often - not too far down the M4 for you that... If you buy a caddy (not a VW!) yourself seperately, make sure its one that can take (laptop) 2.5" and (PC) 3.5" SATA disks, they will then just literally slide into the caddy without any messing with cables and clip in (like 10 second job!).