Thanks everyone for your input. I will get the pool guys to suck all of the water out behind the liner and see what happens.
It is an in-ground pool - just not backfilled. We sank the pool down into the ground as our lot is uneven - that is why some of it is sticking out a bit. It is now backfilled with crushed stone and graded and it is in-ground. Now awaiting cement.
Andy