Note: if the exemption lapses without a new one in place (or a license purchase), they will actually send goons to 'investigate' after a short period.
[0] https://www.tvlicensing.co.uk/check-if-you-need-one/topics/t...
Their "officers" are private individuals employed by a private company who have no special rights to enter your property. Absent a search warrant, it is almost certainly a mistake to allow them to enter your property.
I've given up telling them -- it's less effort to drop their letters in the bin, and appears no less effective at stopping new ones arriving. That was after being "visited" a few years back and the goon trying the classic "if you've nothing to hide".