Many thanks to you all for your replies!I have been to see the dealer who is good with advice ,he seems to think it will be a sensor problem, just clean not replace.I hope he is right as a new sensor is £100!!!The over voltage relay is only £40 so if the problem persists it maybe worth a try now I know where it is!The light did not come on today whilst I was driving but it came on whilst my wife was so it maybe just her imagination(wishful thinking!).The OVR definetly has a replaceable fuse,yes?
Again thanks.
Hamish