Temoraryk of Power

Just been out to do a bit of shopping and on the way there the bike had a distinct lack of power. In neutral the bike reved as it should but just wouldn't "pull" when riding along

On the way back it ran completely normally

Since it was cold and a bit damp on the way out, the best I can come up with is carb icing which melted away when I stopped the bike

Anybody else got a better suggestion for this

Cheers