I know that this will raise a few smiles .... but try Tesco - they currently have deals that take some beating ... core2, vista decent ram .... not future proof ... but for the money a good deal.
http://direct.tesco.com/q/N.1999033/No.10/Nr.9 9.aspx
another alternative is aldi
http://www.aldi-stores.co.uk/
they are the skodas of the pc world - not sexy ... but when you stop and look - they are actually quite a good deal.
Even the PC mags (this month's computer buyer) are starting to take notice of these unlikely sources