The new Alex Rider book is available at Waterstones for £7.96 (And on Amazon). With free P&P.
Also in Waterstones, Piccadilly Anthony Horowitz will be signing copies if you buy them there:http://www.waterstones.com/waterstonesweb/displayDetailEvent.do?searchType=1&author=Anthony|Horowitz
If bought online however you get: 8% Quidco (and a 10% off voucher code)
Release Date: October 31, 2007
To confirm, the price is £7.69 so £6.92 including P&P from Waterstones if you use 10% voucher.