Called family in the Vale of York for their update [they're a few miles south of Leeming]. An interesting point was raised ...
It seems that after crops have been harvested, the farmers don't plough deeply any more ... just the top few inches. It's apparently quicker and cheaper that way. So the substrate remains as firm as ever, and thus less able to act as 'blotting paper' and facilitating run-off. Apparently they started doing this only fairly recently [5 years?].
I have no idea ... I don't have an agricultural background, and nor do my family 'oop there. But it could be a partial 'self-inflicted injury'. Would be interested to hear from any 'gentleman farmers' on here.