Zanussi Washer Dryer Beeped 3 Times

I switched on my Zanussi washer dryer today and instead of coming up with the usual display of the time for the cycle, it beeped three times with the timer flashing zero and the "door unlocked" symbol showing. After about 10 seconds it beeps three times again, with the timer flashing zero constantly.

This is exactly what the machine does at the end of its cycle before the door is opened...

I've tried opening and shutting the door a few times, to try to tell it the cycle has finished.

I've tried switching it off and back on.

I've tried pressing the start/ stop button (and every other button).

I've tried unplugging it and leaving it off for a while to clear any memory.

None of these have made any difference to the problem.

I've read through everything I can find (here and elsewhere online) and have turned up nothing, so any help would be much appreciated.

Thanks in advance