OK, so, I folded the seats down, got in the boot and watched for leaks whilst someone put the hose on the back of the car for ages.

I couldn’t see or hear water coming an anywhere and the boot didn’t get any wetter?

Before I got in the boot I emptied it including the spare wheel etc and the towel that my GF keeps in there was soaking wet.

The car hasn’t been driven on wet roads.

Any other ideas before I remove the bumper as that’s a big job for useless olde me if it’s not that?

A mechanic friend suggested trying a smoke machine in the boot (used for engine bays usually) to see where the smoke escaped to?