Solved! hope this is helpful to others:
The catch was not pressing firmly enough on to the 'interlock', which is the bit just inside, bit like the keyhole, which the catch sits in. Because of this the interlock was not locking. The problem may be with the catch or the lock but eitherways The solution was to press the interlock down manually with a pencil, this sets off the maching and when you close the door it locks shut as normal and un-locks after the wash, as normal.
Jonathan, November 2008