Thanks for the replies. I don't wish to disclose the airline/airport just in case it is condensation as you suggest. I didn't see a walk round but I don't think we would have seen it as we arrived by bus on a remote stand.I do take this flight regularly and always take 12A and I've never seen this on the wing. It was clearly white and during the take off roll it remained undisturbed. The plane climbed without any issue although it was only around 50% full. Driving to the airport there were intermittent heavy snow/sleet showers with frequent cloud breaks. By the time we boarded darkness had fallen and we had clear skies with no clouds. It felt very cold but I couldn't accurately state the temperature. When we landed in clearly much warmer conditions (+5 degC in the car) then you could only see moisture drops on the wing that is normal. To me it looked exactly like the frost that begins to appear on your car when the temperature drops below freezing late on a clear evening. The pilot told the stewardess that it was frost due to recent refuelling which she relayed to me. Although not necessarily relevant I was also a little surprised that the pilot didn't make any type of welcome announcement or any other announcement either before during or after the flight although I suppose he's not obliged to do so.