if you've got the money £125-£150 just go to cyclefit in covent garden or mosquito in islington, and let them do the hard work, for a couple of hours, you'll get the exact dimensions for getting a bike built up from scratch as well as knowing the dimensions you actually are so you can adjust any bike (within reason) to you...
also there have been a couple of threads on sizing which you can peruse for info as well
van just found these links to bike sizing, so you can do it yourself, lots of different sites
http://www.cyclemetrics.com/Pages/FitLinks/bike_fit_links.htm
if you've got the money £125-£150 just go to cyclefit in covent garden or mosquito in islington, and let them do the hard work, for a couple of hours, you'll get the exact dimensions for getting a bike built up from scratch as well as knowing the dimensions you actually are so you can adjust any bike (within reason) to you...
also there have been a couple of threads on sizing which you can peruse for info as well