How can I fix my Beko WMA 665 W washing machine?

My washing machine will start on a wash cycle i.e. it fills with water, but as soon as it reaches the point where the drum needs to rotate it stops. I've been able to drain it by holding down the 'Start/Pause/Cancel' button, and got the washing out eventually, although it takes much longer than usual for the door to unlock. When trying it on a spin cycle (with the washing still in), it makes a whirring noise but the drum doesn't move. I've tried cleaning out the pump filter but this has made no difference.

Alex, Oxford
February 2011