Well I'm delighted to say that 'normal service' has been resumed on the internet front here on the farm.
About lunchtime today (Sunday) a white van pulled into the yard and delivered a parcel from BT containing a '4G Mini Hub - so I spent a little time pointing various wireless devices at it, got it all configured, and settled down to watch an episode of 'Death in Paradise'. Just at the crucial moment in the episode, the land line rang. 'BT Here sir - your line is now working' . It turns out as I had suspected, the BT termination box into which we connect (1.8 miles of copper) had indeed been inundated and ceased to work. He warned me that things are likely to start and stop a bit for a few days as many cables need replacing / rewiring.
So I enjoyed using the BT supplied Mini Hub for about 20 minutes ! But Well done to BT for sorting the issue well ahead of their initial estimate of Wednesday or Thursday at the latest. Far better than setting a short timescale and missing it - managing customers expectations we used to call it !
Quite impressed with the Minihub- - handy to know about and apparently it's now mine to keep, though no doubt BT will turn it's SIM off in due course