Sounds like hoar frost forming on a cold soaked airframe.Might well have formed after landing.How long was the flight?
The flight was 1 hour, did a few circuits. It may well have formed after landing - that is quite a possibility and also why I didn't notice any whilst frequently checking the wings and struts during flight. (Also would explain the lack of degrading performance which would be expected if ice was on the wing)
Carry a can of car windscreen deicer even for a little its not good practice to attempt a takeoff and at what point does a little become a little too much ?
Should there have been any frost on the wing prior to departure, I would either have deiced, or cancelled the flight without question. I was under the impression that takeoff with ANY ice on the wing was prohibited. Very good point about the little and the too much though!
Step Turn & Piperboy84 - neither did I - that is why I was so surprised!! But Dash6 makes a good point, perhaps there was a little more moisture when I landed and it just created a thin layer of frost after landing. The surface was clean and dry on takeoff (if a little cold to the touch!)