If you were the military decision maker with responsibility for defending the UK's airspace and you were presented with an aircraft approaching the UK either not in communication with ATC and/or with anomalies on its flight plan and it had originated from a country south of the Sahara, what would your prudent decision be?
I understand it's not the first time that this scenario has happened this year. One wonders how such aircraft make it all the way across Spain and France without them taking some form of action...
Unlikely but not unknown for the Typhoons to go supersonic over land, but this is usually on the way to intercept.