There are definitely areas of the UK where there are wild living colonies that have learned to live with Varroa.
Beesnaturally has many posts talking about his own experiences with treatment free. He knows what he’s at. To a far greater degree than many on this forum that think they do.
The genetics of these bees are most likely quite mixed. Ideally beekeepers in these areas would introduce Amm colonies to their apiaries and start to move the entire population back to Amm.
I remember reading in a paper by Victoria Buswell that the genetic makeup of bees in parts of Cornwall had moved back to largely Amm in the space of time separating two sampling rounds. I guess that reflects the work of groups like B4.
https://www.b4project.co.uk/
The UK just needs more groups working together like this. I’ve referenced this before but I did find Willie Robson from Chainbridge Honey saying he was looking at an Amm Queen Rearing programme very heartening.