OK, your stated budget is £500 or $806US. Since I know my setup works for XP as well as Win 7 and 8.1, I would recommend something similar:
Mobo Gigabyte GA-Z77X-UD5H $200
CPU Intel Core i7-3770 (not -K) - $290
unless you insist on overclocking, the K version gains nothing and loses some virtualization features.
Memory: I'm running 32GB of Kingston Black 1600. You need at least 16GB. For best performance, fill all four memory slots.
4x4GB - $150 - $200 $156
PSU - Antec EA-650 $ 80
Disk: 1TB WD or Seagate $ 80
Total $806US = £499
All prices are current Newegg US
You can probably get better prices if you do a little judicious shopping around, and look for sales.
Memory prices have gone up since I bought mine (June 2013). Tiger Direct sold me two 2x8GB kits for $114.99 each or $229.98. They're up to over $300 for the same thing now.
This assumes your case is usable (ATX compatible).
If you want super graphics you'll have to add a good video card. The HD4000 GPU in the i7-3770 is pretty good for general purpose stuff. I'm running 1920x1080x60 very nicely on it. A graphics handler (switcher) program is included on the driver disk.
The Gigabyte board includes provision for a bootable mSATA SSD on board if you wish.