What do you have already? I take it graphics, screen, etc.?
An entire SFF with an e6600 for £300 is pretty much impossible.
Hitachi Deskstar T7K500 NCQ 250GB SATA-II 8MB Cache - OEM £32.99
(£38.76)
Intel Core 2 Duo E2160 "LGA775 Conroe" 1.80GHz (800FSB) - Retail £51.99
(£61.09)
Antec NSK1300 ATX Cube Case - 300W PSU £49.99
(£58.74)
Sony DDU-1615 DVD-ROM (Black) - OEM £9.99
(£11.74)
GeIL 2GB (2x1GB) PC6400C5 800MHz Value DDR2 Dual Channel Kit (GX22GB6400DC)£49.99
(£58.74)
Asus ATI Radeon X1050/TD 128MB HyperMemory TV-Out/DVI (PCI-Express) - Retail £21.99
(£25.84)
Abit IP-95 Micro ATX (Socket 775) PCI-Express DDR2 Motherboard£31.99
(£37.59)
Sub Total : £248.93
Shipping cost assumes delivery to UK Mainland with:
City Link Parcel Next Day (Delivered Mon-Fri)
(This can be changed during checkout) Shipping : £9.95
VAT is being charged at 17.5% VAT : £45.30
Total : £304.18
Best I could do, of course if you have a DVD drive, graphics and HD already then you're a lot closer to having an e6600. If you wait until July 22nd there should be a price drop on the Intels.