This is not referring to the central locking, but the individual door lock.
Its on the drivers side - When the key is in the lock it rotates both ways, but with no resistance - And does not lock or unlock the door.

As the key goes in and rotates id assume that the barrel for the key is ok and that something has come lose between the two points??

Ash J, April 2010

Cheers mate, im an aircraft fitter so used to fiddly things. Il see how I get on this weekend.

Ash J, April 2010

You will have to take the inside door panel off,the key hole is connected to the lock mechanism with a piece of wire coat hanger bent over at both ends and usually held in place with a plastic clip(bottom end)or just hooked over back of lock(top end)fiddly but dead simple when you take door panel off,it's not difficult just fiddly,fiddly fiddly,once you crack it you can fix most car doors,they mostly work the same way.Easy peasy,good luck,be patient.

a, April 2010