The Camelbak Cloudwalker is £24 (with the 20% off Bank Holiday promotion) at Field and Trek, with delivery at £3.99. I think it's free delivery if you spend over £50.
It seems like a pretty good deal - Evans Cycles have it for £34.99 delivered.
This seems to be the 09 version, the latest 10 version is £45 before the discount.
It may be available instore too.