Most certainly there are feral honeybee colony sites.
Bees colonising the sites are from the local population, that would in the majority of the UK from managed ( or mismanaged!) colonies.
Now what do you call a swarm that moves into an empty or bait hive?
Would honeybees left totally to their own devices develop a resistance to varroa and the virus they transmit to the bee?
I think they would if they could survive long enough AND there was no introgression from contact with imported bees.
( and by imported I mean bees introduced from outside of the "isolated" community)
BUT (sigh) this will probably not happen !
it is always said no AMM is found in London but there is a colony of Honeybees in a small wood near my house in North London that are black and hairy with a negative Discoidal shift, i have had bait hives out but no luck
I have trapped a few individuals to measure wingsand def negative, The nearest beekeeper has a very dark bee but it is only just negative shift
I also know of a "large and hairy" black bee with a larger negative shift in a stable chimney near South Mimms, M25 jnct 23, The estate owner said they have survived for many years and produces two swarms a year on OSR.This spring most of its daughter colonies had died over winter ( i had hope to cut one out from the eves of a barn)
But the chimney colony had survived but did not swarm this year However a new beekeeper in the area has rather yellow bees
whereas other local beekeepers bees are at least black
If i catch a swarm from either colonies I was wondering if they could be nutured together but that would mean moving one 10 miles (North London one) , /now is that to far to be "local"
it is even in london with it horrendous mix of sub species of bees ,quite noticiable that the first bees and last bees feeding or collecting pollen are always the blacker mongrels while the yellow italians stay at home