On xmas eve it developed a fault where it sounded like it was working
correctly, but the drum did not revolve.
It fills and drains, makes all the correct noises, but the drum does
not move.
I can move the drum easily by hand.

IF you spin the drum by hand (fast!) does it feel like it is connected to a
motor?
(Try spinning a working washer to hear what it sounds like!)

If not, then I suspect the dive belt as others have
If you do hear the motor spinning, then either the motor, motor controller,
or interconnecting cables have failed!

How old is the washer?

Sparks...