http://www.chainreactioncycles.com/brand-x-rd-01-road-frame-and-carbon-fork/rp-prod130456
would be a quick donor model, but I’d sooner hire one.
cycledivision sell cannondale bikes that are often reduced – legit company despsite their website.
I think you need to consider places where you can walk in and leave with your bike. With that in mind, have a look at Evans, Halfords, Decathlon if they are near to you. The top end stuff from all of them looks nice – BC discount means it might be worth joining online to save some money.
If you look on facebook you might have a local for sale section. One near me (CDNE bike sales) has some good bikes on. When mine was broken and I was looking at missing races I considered buying a second hand £500 one. Would have been ok (carbon/tiagra) and could have sold it on or kept it as a winter bike.
Final one, risky buying mail order with this little notice.
http://www.bikebargains.co.uk/bikes/