I don't know about a UK (since I only wear tartan), but if you wear a tartan kilt you might want to think trough a small thing: I flew from Scotland, via London and to Norway two weeks ago. As usual I did wear my kiltpin. In Scotland it was fine, in london I had to wait for them to telephone their boss to approve I was wearing it because of the sharp ende, treathning object, etc. Back in Norway I can't even fly with it attached to my kilt. So be a little carefull when wearing a pin, and have a backup plan in case they stop you.

Otherwise, flying with kilts are a very plesant experience.