So my car has been in to see a trusted mechanic a couple of times and now he is 99% sure it is solved and that water was coming in via the rear near side light cluster. Although the light unit looks ok and the foam seal was undamaged it simply wasn’t doing its job. There is a square gap where the wires come through but no seal of any sort. With all the trim inside removed and a wet day to test on, it was easy to see water draining down into the section behind the trim and also down into the tyre well.
the solution has been to add some extra foam to the seal and I initial testing has proved successful. It will be interesting to see the reduced condensation and a dryer boot.