Done! Drivers side wasn't full of water, but the pipe was partially blocked with some slimy lump, so probably wouldn't have stayed clear for much longer.

Anyway, both sides now clear; checked the drains under the bonnet while i had the compressor out, all seems ok - no standing water in there, quite a few dry leaves in there so blew them all out just in case.

Passenger side carpet now slowly drying out in the garage in front of the calor gas heater!