If you are approached by somebody offering for sale a bike similar to the one on the left, do not part with any money!
These are bikes are cheap imports which do not comply with British Standards. The bikes are quite unstable, have rather thin frame tubing and are prone to flat tyres.
You have been warned!
[img]http://www.edmontoncyclingclub.fsnet.co.uk/images/flatbike.jpg[/img]