NOW SOLVED!
It was the relay on the right of the fuse/relay box that I had already changed.... but of course I used a relay that I had previously swapped out when I was advised to carry spares for the Fuel Pump and Injection last year when purchasing the car.
So morale of the story......relays can even fail when there not being used!! (Probably more prone to failing then,in fact!)
Now the fan seems to run all the time (in fact it was quiter when it wasn't :-)
