In reply to Strachan:
Problem with a triple is it never runs a sweet as a double, and cost a lot to convert. If your are worried about gearing, then go for a compact with a descent sized block (most decent shops will swap a standard double for a compact)
My advice to the OP would be to go and ride as many bikes in your price range as you can, as fit & feel are very individual. Read as much as you can in terms of reviews (remembering often bike mags etc are paid to give good reviews so look online for user reviews too) If a carbon frame is out of the price range, consider a frame with a carbon fork as this will take a lot of the road buzz away, which is a great improvement on longer rides.
Also consider getting something second hand, there's an awful lot of people who spend £1500 and then ride the bike a few times before deciding its not for them.
At the lower end, the Boardman bikes they sell at halfords are good value (get someone who knows what they are doing to check it over for you as Halfords haven't got a good reputation for setting the bike up correctly), as are ribble and planet x (both on-line sales only).
Spend your money on a good frame rather than a mediocre one with better wheels, as the wheels are easier and cheaper to upgrade at a later date when you get into it.
Keep some cash back for a descent set of shorts, and shoes/pedals, helmet etc.