Thnaks for the recent replies. I have never removed the dashboard fan switch and I'd be very surprised if previous owner had. Moving the air control **** does re-direct the air to the relevan vents, it's just very weak flow from all outlet vents
If I press the recirc button, something happens inside the dash as the noise changes completely but flow does not incerease.
I removed the scuttle plate and checked that the air intake was not obstructed, all clear.

It's as if the main route from the fan output is restricted in some way ?

I have replaced the battery, so will check I haven't cruxhed the vacuum pipe.
Mick