What PSU should i get?

Look for a quality unit around 500W, such as one from XFX, Antec, or FSP. You may need to stretch your budget a little. A PSU is not something to try to get cheap; the long term health and stability of your system are dependent on a quality PSU.
 
a good 450w+ will do but why not get an amd cpu so you can get a better GPU? here is a setup which will better in gaming and also editing.

PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: AMD FX-8350 4.0GHz 8-Core Processor (£143.99 @ Aria PC)
Motherboard: Asus M5A99FX PRO R2.0 ATX AM3+ Motherboard (£106.99 @ Amazon UK)
Memory: Corsair Vengeance 8GB (2 x 4GB) DDR3-1600 Memory (£59.97 @ Amazon UK)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive (£48.36 @ CCL Computers)
Video Card: Sapphire Radeon HD 7950 3GB Video Card (£219.76 @ Amazon UK)
Case: Corsair Carbide Series 300R Windowed ATX Mid Tower Case (£70.97 @ Amazon UK)
Power Supply: XFX 550W 80 PLUS Bronze Certified ATX12V / EPS12V Power Supply (£49.86 @ Scan.co.uk)
Optical Drive: Lite-On iHAS124-04 DVD/CD Writer (£12.98 @ Novatech)
Total: £712.88
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-09-12 22:49 BST+0100)

a little over budget but you can get a cheaper case, HD ext... if you like
 
PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: Intel Core i7-4770 3.4GHz Quad-Core Processor (£234.90 @ Amazon UK)
Motherboard: ASRock Z87 Pro3 ATX LGA1150 Motherboard (£91.37 @ Amazon UK)
Memory: Corsair Vengeance LP 8GB (1 x 8GB) DDR3-1600 Memory (£53.00 @ Ebuyer)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive (£48.36 @ CCL Computers)
Video Card: MSI GeForce GTX 760 2GB Video Card (£188.99 @ Aria PC)
Case: Zalman Z5 Plus ATX Mid Tower Case (£38.99 @ Novatech)
Power Supply: XFX 550W 80 PLUS Bronze Certified ATX12V / EPS12V Power Supply (£49.86 @ Scan.co.uk)
Optical Drive: Lite-On iHAS124-04 DVD/CD Writer (£12.98 @ Novatech)
Total: £718.45
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-09-12 23:00 BST+0100)
 
My budget is only about £700. Including monitor, periphals and os which will take up about £190. So i need the CPU, motherboard, RAM, GPU, Case, Dvd drive, HDD and PSU for about £510. Any ideas?