Mine was doing this and after a bit of searching around I found it to be the heater element.
To get to it, disconnect from mains, remove the plastic cover from the bottom rear of the machine and the element is on the right hand side of the bottom the tub. With the wires removed, you can test for electrical continutity or earth leaking with a multimeter. In my case a wire was not fitted correctly after an engineer visit a few months earlier, when they changed the whole drum. The wire was missing its spade connector and dropped off. It showed signs of melting... not good. Anyway my element was fine, I fitted a spade connector to the wire, re-connected it and it worked first time. New elements are around the £40 mark and look easy enough to get to.
Mark Sangster, March 2010