One of three choices - Nikon, Canon EOS, or Pentax - Go for a system that shares the same lenses between film & <cough> digital bodies. You'll need to do a little research on the available lenses, but certainly steer away from the Canon EFS lenses as they will only fit the digital bodies.

Find yourself a reputable second hand camera shop (maybe London Camera Exchange) and see what they have in stock and can recommend - What ever you do, do not visit Jessops for unbiased advice.

Oh, and don't mention the "digital" word here unless you want a late night visit from Professor Abraham Van Helsing...