?photo editing?
I’d bias that towards a £200 monitor, a reasonable AMD APU and a pair of big HDDs with a backup system.
http://www.tomshardware.com/reviews/amd-a10-7890k-gaming-performance-benchmark,4491-5.html
7890 or 7870k? Built in graphics very useful, will accelerate some other tasks (Photoshop, transcoding), can do some gaming and will also allow a low end graphics card to be added later, where it can work together with the APU for a cheap gaming boost.
That article has some suggested components, and the Ars Technical or Tom’s Hardware budget builds will be great references too.