Thank you for all the replies. I'm inclined to rule out badgers because, apart from the fact that I've seen no sign of any round here, most of the plants were still half standing but with some tops broken and hanging down, and the cobs weren't on the ground; they were still upright. I also haven't seen a squirrel for a couple of years and there seemed too much trampling under foot for squirrels. I suppose that leaves deer - and deer bigger than muntjacs.
That would be the first sign of roe deer around here that I'm aware of. Quite exciting apart from the need to create a fortress round the sweet corn next season.
Interestingly, slightly earlier corn had remained intact over the previous month, and had been picked and eaten, so this was something passing through rather than a regular visitor.
Janet G