I'm not a member, do people just use membership for insurance? I can't understand why they would join an organisation they find so useless if this were not the case.I know there will be staunch BBKA members tutting at this, I know of one at least and he is adamant bees survive equally without. As a trainer I have heard him tell others he has never done so, so it isn't necessary, imho a non thinking beekeeper stuck in the trenches of old BBKA thinking.
I could show you colonies that survive equally well without insulation. We had no Winter loss this year, I would say about 40% in battered, old boxes due for repair (or replacing) with no insulation. They all had the same treatment and feeding regime, two were heavy enough on Ivy so got no invert. One of those was huge on first inspection and still had half it's Winter stores.
My friend runs his apiaries entirely without insulation and he doesn't lose colonies.
Should add we both use poly nucs but more for convenience and price.