Yes, I have. It was at night, and it was three points of light, about mag 1 in brightness, if they were stars. They were configured in a triangular shape. It was moving silently from east to west, (about 15 miles south of Glasgow.)
Of course I thought about Aurora. There was a reliable sighting over the North Sea a long time ago.
http://www.firstscience.com/sit e/articles/aurora.asp copy
I also considered that I live between the North Sea and Machrihanish airbase, (the UK's answer to area 51.)
http://www.dreamlandresort.com/ black_projects/machrihanish.htm l copy
I know that both the American air force and navy were stationed there for a while, and it was rumoured that a number of "black ops" projects flew out of there. In fact there's a theory going around that the chinook crash on the Mull of Kintyre, (a few miles from the base,) was caused by the Aurora. I think that's totally fanciful.
http://www.theregister.co.uk/20 00/07/10/top_secret_us_plane_ca used/ copy
However, I live under one of the main approaches for Glasgow airport, so I doubt anybody would be flying an allegedly invisible plane through that airspace. True, they would be able to see the other air traffic, but it seems irresponsible.
Anyway, I don't suppose I'll ever find out what it was that I saw. I'm not driven to find out, and I really don't want to sound like a crank.