"!If your job involves being outside in winter then I could see how this would be a legitimate expense"
I think the test you have to be able to establish that the woo;y underwear was totally work related and that it could not be used for non-work use as well .... seem recall there was a case where a female barrister tried to claim her court clothes as a work related expense on the basis that she wouldn't wear clothes with such "conservative" style and colour outside court but she lost as HMRC tribunal ruled that just because she said she wouldn't wear that sort of clothing outside court didn't remove the possibility that she could so the clothes weren't "for work only" and thus weren't a deductible expense.