The only people still flying them is India. Unless there's a privately owned one knocking about I dobt it was a Jag. I live right under the low fly route in the southeast and it certainly has never turned up here. Maybe an Alpha Jet?
The only other thing I can think of is a Mirage F1. They were supposed to have finished flying in July after their final fly past over Paris. Could it have been a straggler being ferried to storage?