Richard - you are an absolute genius! I used the manual release under the filter flap, and opened and closed the door (slammed it right and hard!) 5 times.
Turned the power back on and the machine now works perfectly, as it did before!
Have you a favoured charity at all? I'd like to make a...
I have an old W828, has served me well - I did have the flashing "check inlet" light problem, so ordered a known good used board from Ebay - the fault then resolved itself before the new board arrived, so I have a spare control board!
Problem - did a wash as normal, everything fine. Next time I...