A hose in the engine is frosting up (like you may see in a fridge - see image - the hose/pipe is not normally white!).
Any ideas what this may mean?
I've also losing some coolant in the radiation (..but that maybe unrelated?).
That is totally normal. It's the AC line from the orifice valve to the evaporator (inside the cabin) which is supposed to be cold. It's common for these to frost up in humid conditions.
get your car ac expansion-valve checked by a qualified mechanic. if you had never seen that earlier in your car, get it checked for proper refrigerant pressure at both high and low sides.
