What do you do when the freezing level is below MSA?
Probably, you don't go. That's the price for not having a Gulfstream, or a 747, basically.
When you're in the climb how do you know where the tops are? - often the cloud goes higher than unpressurised aircraft!
You do proper flight planning. Get skew-t charts for locations enroute, etc.
Being UNpressurised is not connected with the operating ceiling. You just get the oxygen on. Plenty of unpressurised planes will go to 25k feet which is above 99% of stratus cloud, and the other stuff one has to handle differently.
I have never asked for a climb due to ice as I've never flown in icing conditions in other than a anti/de-iced aircraft, but I have flown in de-iced types, so can agree that often it's a short lived problem; but not always, sometimes it's wore than you expect.
Yes, it's a case of doing the planning properly, and keeping escape routes open.
I am not saying it's impossible to operate an aircraft without ice equipment in the UK in winter, but I am saying it's not easy in terms of judgement and knowledge, and demands considerable experience. Bose, you obviously have this experience and knowledge, but has Brian304?
He may not, but one can always learn from those that do it. You probably aren't going to learn how to get a TAF off the internet from the average GA instructor, let alone how to get the more obscure stuff.