Possible causes
 

Whilst flying back to Liverpool yesterday from Carcassonne the plane suddenly rolled (approx 45deg) to the left quickly enough to cause the cabin crew to stumble and grab on something. The plane then recovered and all seemed normal. Whilst we disembarked two mechanics were looking at the fan blades inside the left hand engine. Is it possible that an engine surge caused the plane to roll suddenly or is it most likely a wake encounter?

Not a surge but maybe wake, or just turbulence. Happens all the time mate.

The inspection of the engine could well be coincidental to the unexpected change in attitude. As they say, 'Please keep your seat belt loosely fastened at all times.' :uhoh:

High alt bird strike? Goose maybe? Engine is designed to take it, and the pilot may have seen it coming if they were lucky, which explains the roll. A stall/sturge wouldn't have produced enough yaw to roll the a/c 45 degrees uncommanded.

Could also have been a trim runaway with an a/p disconnect.