My £550 build, are the parts compatible and would you change anything?

You could switch some things around to fit a 7870XT (basically a 7950LE) in there:
PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: Intel Core i5-4440 3.1GHz Quad-Core Processor (£132.08 @ Ebuyer)
Motherboard: ASRock H87M Pro4 Micro ATX LGA1150 Motherboard (£60.00 @ Amazon UK)
Memory: GeIL EVO CORSA Series 8GB (2 x 4GB) DDR3-1866 Memory (£60.99 @ Amazon UK)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive (£41.00 @ Amazon UK)
Video Card: PowerColor Radeon HD 7870 XT 2GB Video Card (£152.44 @ CCL Computers)
Case: Corsair 200R ATX Mid Tower Case (£47.98 @ Dabs)
Power Supply: Corsair CX 430W 80+ Bronze Certified Semi-Modular ATX Power Supply (£37.10 @ Amazon UK)
Total: £531.59
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-12-20 22:54 GMT+0000)

or if you want a mATX build:
PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: Intel Core i5-4440 3.1GHz Quad-Core Processor (£132.08 @ Ebuyer)
Motherboard: ASRock H87M Pro4 Micro ATX LGA1150 Motherboard (£60.00 @ Amazon UK)
Memory: GeIL EVO CORSA Series 8GB (2 x 4GB) DDR3-1866 Memory (£60.99 @ Amazon UK)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive (£41.00 @ Amazon UK)
Video Card: PowerColor Radeon HD 7870 XT 2GB Video Card (£152.44 @ CCL Computers)
Case: Cooler Master N200 MicroATX Mid Tower Case (£31.33 @ Amazon UK)
Power Supply: XFX 550W 80+ Bronze Certified ATX Power Supply (£47.12 @ CCL Computers)
Total: £524.96
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-12-20 22:57 GMT+0000)
 


HD 7870 XT: System Requirements Minimum System Power requirement (W): 500W
 


It would be completely fine, you can check on a PSU calculator, but if you want to be safe, you could mix in the PSU in the second mATX build I posted :)

The 7870XT is based on the 7950 reference board
 


They have almost the same gaming performance, the 7870XT ~ 7950 ~ GTX760 never mind the more single thread efficient i5-4440. And it costs £30 less with a better case.