Graham
Thanks. Will check that out, but I dried out the footwell this morning, have just driven down to Maidstone and back to Orpington and it's full again! No rain, so I am guessing it might be something to do with the aircon - I was running that on full heat to try to dry out the carpets???
I'm not very mechanically-minded (can just about open the bonnet!) so this is probably a dumb diagnosis, but I can't think of anywhere else in a car that water can be leaking from - other than the water container for the wipers or the radiator - the former is empty and the latter seems to be OK.
Ian