I have finally fixed the problem (having to do the washing up again today was a great motivator!).
It was the timer!
A (solid core) wire is spot welded to a spade connector on the timer, this wire is then soldered onto the motor that runs the timer. The wire was broken off at the spot weld on the spade connector. From the looks of a very small burn mark on the spade connector my guess is that this wire has always been broken off and was held against the spade connector by its own "springiness".
I think that this machine does not "know" when it is empty, but merely relies on the drain pump being turned on for a set amout of time (I have found this out the hard way - I have had the machine to bits, and everything checked out fine).
Thanks for all the suggestions.
Paul