At last. After months and months of no light, a change of relay and a selection of fuses and the Nippy Norman mini-spots are finally working again.
The blown fuse was 7.5amp. I emailed Nippy Norman to ask what fuse ought to be in the holder and they replied that it depends on the current being pulled through. I thought as they put the kit together they may have been able to say!!
In the end I reckon the lights are maybe 55w each, so two will be drawing 110w @ 12v so maybe 9.166666amps? I've bunged a 10amp fuse in. So far so good.
It's a miracle.