If you don't really need the latest processor, and want to go look Intel, you can do a lot cheaper if you go for a socket 775 MB. Those Dual Core process's really aren't that bad. You can find lots of simple but decent MBs with PCI-Express for around 60-70 USD And Dual Core CPU for around 70-80 USD.
Not sure if they sell or what options they are to ship to the UK(Assuming that as you said 150 pounds) But places like tigerdirect have combo MB's and CPU for ~100-~120
Sure you will only have 1 PCI Express x16, and probably just two DIMM slots, but do you need expandability? Heck you can get 2x2gigs of RAM cheap. I speed isn't the big concern I'd stick with a socket 775 mb and CPU