1998 Peugeot 306 Horrible noise coming from engine

Hi, 2 days ago i had my cam belt changed, today was the first time ive driven my car since the fixture, i drove about 15 miles and this horrible rumbling sound (like a very loud tractor) starting coming from the engine... ive been told its possibly the head gasket? I need to drive to work tommorrow, please could someone give me some clue as to what it coulkd be.

Thank you