It's not really about the fuse in the incomer, though. A 70's delivery network was probably designed with an overnight diversity of between 1 and 2 kw per house, and the fact they were fitting 60A fuses might indicate that it has got worse than that since. That'll all be absolutely fine when everyone's got a milk float on charge overnight, of course.
Electrics aren't my strong suit, I can wire a plug, know how to run cables to keep building control happy, but diversity loses me a bit.
Kevin, can you explain why you would have night time diversity that's different from peak, say when everyone turns on their oven, shower or kettle, which 80% of people do at the same time.
Even if I get a 7kw wall box put in, that's still pulling less than when I have a shower, (9kw) or more to the point at 645am when loads of people put the shower on.