Thinking that 6Ltrs of water in the passenger side meant blocked holes between the scuttle and the wheel arch resulting in water ingress via the pollen filter and a drowned carpet, I cleaned out the scuttle area and pushed the fillers back into the voids in both wings as they had moved forward almost blocking the drain holes. That wasn't the problem. It turned out that the passenger side front door window seal had somehow dropped away from its position in the door frame around the top of the glass. When I opened the door there was a splosh of water all over my shoes which I didn't understand until I noticed the re-positioned seal. The car had stood in steady rain for three days. The carpet will take longer than that to dry out. I've put the front seat on the back seat and managed to get under the carpet to squeeze out the foam under the carpet, but what a job! Does anyone know how to remove the lower 'center pillar trim' without breaking it, as with that off, carpet access would be much easier.

Update. It wasn't the door or window seal because it just happened again. I discovered that the water was entering the car from high up behind the trim that fits to the left of the front passenger's feet. Very difficult to get to from inside the car. We took the wheel arch liner off and found that there is a rubber bung that pushes up into a void inside the wing. Water pours down into the void from the scuttle and muck eventually totaly blocks the drain. Over time, the void fills up and the water over-spills through a hole into the passenger foot well. I bailed around four liters of water out of the rear foot well and am once again drying the soaking carpets, front to back. The photo, 'blockage 4' shows that the driver's side was also almost blocked with grot. The answer is to blow out the void with an air line.