Water flowing from cistern into pan!
Remove cistern lid by unscrewing the flush button by hand.
Turn off water.
Remove flush assembly by pressing in sides, at front and back of flush assembly base. As it comes free remainder of water in cistern flows into the pan.
At base of flush assembly there's a round seal which will be covered in blisters, and these should be poped to make the seal flat again.
Refit seal, flush assembly and cistern lid.
Peter from Manchester, July 2015