Someone at the airfield where Toppers landed probably got mixed up between operational hours and licenced hours. An airfield (runway) can only be licenced while certain conditions are met, eg particular level of fire cover, and if this isn't present because the staff haven't yet arrived then the airfield is unlicenced. This should be of no practical or legal consequence for a non-training private flight.
Operational hours, on the other hand, may be limited by local planning restrictions, e.g. no movements before 0900 or after 2100. They may even be limited by the whim of the owner or manager, in which case it could be argued that you didn't have permission to use the airfield at that hour.
It is very easy to fall foul of restrictions like this in spite of telephoning in advance because the answers you are given often seem to vary according to who answers the phone. It can often be easier to get permission to land early in the morning at a farm strip than at a licenced airfield. Only in the UK could we arrive at such a situation.
I'm told that in the USA most small town's airfields are what we would consider unlicenced and are always available.
I have never seen any restriction on a private aircraft insurance that limited the use to licenced runways. Perhaps if you had something very expensive (DH Mosquito?) you might negotiate a reduced premium for such a restriction but none of the policies I've had have ever had such a restriction.