In the Scotts of Stowe catalogue that fell out of yesterday's paper was an illustration of something that they call Rope Caulk, which looks as though it might be just the job for your draughty windows. Unfortunately their website refuses to admit that they stock it, but a google search was much more helpful.
http://www.scottsofstow.co.uk/Reusa...oductFeed-_-Product-_-1609886&source=googleps
http://www.scottsofstow.co.uk/Reusa...oductFeed-_-Product-_-1609886&source=googleps