I don't know UK prices, but even at a 1:1 with the US dollar that shouldn't be too hard.
Do you already have the monitors? Honestly that's half the equation with photo editing.
Other than that, I'd go with an Intel i7-3770, H77 board, 16GB of RAM, a good sized SSD for OS + Apps + scratch disk and then another 7200RPM disk for photo storage. Case and power requirements should be simple.