jackg

Well I solved the problem.
It is a very simple pair of contacts in the fluid lid and a small metal washer on the end of the float in the lid.
If you push on the round end of the float the contacts are pushed upwards and make the warning light more likely to come on.
I stripped the lid of its three components and straightened the contacts and then reassembled the lid. Problem was then solved.
The threaded ring is pushed off the lid body.
A pair of snipe nosed pliers is then used the grip one or both switch contacts where the cable connector inserts, and then simply pull the contacts out of the lid body.
The float then falls out.
Straighten the contacts and reassemble, insert the float firstly and then push the contacts back in. The contacts hold the float in place. If the float falls out you have not pushed it in far enough before inserting the contacts.
You can check to see if it works with a multi meter.
https://www.flickr.com/photos/67356568@N05/15982155443/
 
So no warning light on the dash now, clever old me.
Got to go for a drive to allow the ECU to check and correct the error.