james: Not quite sure how to interpret your smiley in this case, so I'll play straight man.

GMT is the local time zone for the British Isles.

UTC is a technically adjusted version of GMT (the difference, generally, is measured in milliseconds), but technically, the time used by airlines, U.S. military, GPS, and time & frequency standard stations such as WWV, WWVH, WWVB, and CHU is UTC. (Probably even Rugby! )