QDM
I was chatting to an owner of an Auster at Leicester who was planning to get his mountain rating this year. He was planning to hire a French instructor/aircraft do the rating and then put skis on his Auster. He seemed to think the UK licence was not a problem, but the rating is at least partly strip specific and has a currency requirement of, I think he said six months.
Good luck if you have a go, I will be very envious!
Rod