Zanussi Aquacycle 800 FLS883W - Clicks through cycle without doing much?

Intermittently, usually when desperate, washer shows unusual symptoms.

On selecting cycle, machine fills OK and then motor spurts into life for a few seconds before stopping for a while. Then it 'spurts' in the opposite direction but again doesn't rotate any length of time. It'll do this a couple of times before clicking through the whole cycle in a matter of seconds, draining and filling at each switching of the timer (ca. 1 sec fill, 1 sec drain, etc.). Doesn't appear to matter what program it's set to.

I've checked the motor brushes to be OK and the pump seems OK, too.

Thing is, it's only now and again (only now just now) and when it's OK, everything works fine and can do so for weeks without a problem.

Assistance appreciated.