Latest update (& solved).

Thanks again for all the advice.

I replaced the heating element and all is tickety-boo.

One thing I did before replacing it was measure the resistance (yes, at low voltage, using my multimeter) between E and the two power terminals on the element. It showed as totally open circuit. Compared to the 500k - 1M Ohm of the old element. (I realise it would have been better to measure at mains but was unable to do that).

So, the washer is fixed (for now!)

Which leaves the strange thing of the RCD still tripping a couple more times after I first unplugged the washer. I didn't imagine that, and of course there could be this high residual current thing that some of you suggest, with the washer just pushing it over the edge. I also wondered if it could be that the characteristics of an RCD change, even if slightly, if it is repeatedly tripped in a short space of time. This making it a little 'sensitive', so to speak, such that even with the washer unplugged it tripped a couple more times.

What do you all think? Seems odd, but it has not tripped at all since and everything is very much back to normal.