Thanks for the replies.
It is a UK car so the side that is wet is NOT the side where the washer fluid is.
The carpet up behind the pedals is dry, so don't think its blockage below the windshield, it is further back around the bottom of the seat that is soaking wet.
Don't have a garage as i live in London, plenty of supercars are kept on the street here and should be able to survive some rain.
Any other ideas?
I have dried it out once already but its wet again....