I have just clocked this on my box (no lat/long) in the Newcastle upon Tyne area at 2140hrs local.
Mode S - 43C4A3
Squawk 5111 (This is a Squawk code from RAF Boulmer)
Went from FL480 to FL390 in about 3 minutes.
I have done a search on google to try and tie it up and it may well be a Typhoon? Anybody able to help out.