Thanks, but weather has been so bad haven't had a chance to try this yet.
I've unclogged drain in front of steering wheel and water is no longer running into the car, I can't tell whether this has solved the problem yet as car needs to dry out.
I had to get further advice from friendly mechanic as to how to get the windscreen wiper blades off (wiggle them, as the connection is conical). Some pictures would have helped! I can't get the plastic cover snug onto the windscreen, is there a knack or should I use silicone to plug the gaps?
I'll rate your advice when I'm sure problem is solved. Thanks so far.