Well I managed to get a good look under the car this morning.
Spotted a rather large hole right under the passenger foot well (which would explain why the gf thought Id driven over something cos she felt a bump)
My theory. Was driving along, and a baffle was loose in the silencer, broke loose, and due to the pressure blocked up the exhaust which caused a build up of pressure and BANG, the exhaust exploded.
Gonna get it checked out tomorrow