Problem solved!

http://www.amazon.com/SHIMANO-TY-22-...1842003&sr=8-1

I have asked a friend in the States to get them for me and bring them over next time he's on this side of the pond sometimes in the new year.

I will then be able to upgrade from 18 to 21 gears - I am finally propelled into the 21st century, not.

However, this now creates another problem: sorting out the best gearing ratio for a commuter, everyday bike, also used for touring/camping trips!