I'd recommend a barebones. That way, you know the basics are assembled and (more importantly) tested before you get it. Novatech, since you mentioned them, do a barebones for around £370, which includes the CPU you wanted, Intel P45-based mobo, a nice case, 530 watt PSU, and 2 gig of ram.
http://www.novatech.co.uk/novatech/specpage.html?BB-P4584S
http://www.novatech.co.uk/novatech/specpage.html?BB-P4584S