After a little frustration I told my son to sit on the boot and managed, with a little force, to turn the key in the boot to get it to spring open (once my son had been removed). As thought, my rugby muppet mate had slammed the boot lid with a web handle of a carry bag across the catch system. It was closed but the soft door was trying to get it the last few millimeters to be tight.
Moral of the story is, ensure nothing is causing an obstruction across the lock mechanism when closing the boot lid!!!!!