Temp gauge sudden rise to max hot but engine & water are normal!

Hi my freelander 4 cyl. 2004 1.8L had a hg replacement under warranty in London. Brought it to Kilmanjaro with me in 2007. Never had a problem with it until recently I often note sudden rise in temp gauge from slightly below half mark (where it always rests) to max hot with warning light on and second fan kicking on. However, the engine temperature & water in radiator would be normal and if I switch off the car for just 1 minute the gauge would return to normal readings & the second fan will stop and then the problem is no more until some future days when it recurrs sudden. Any idea?

Should have left it at Kilmanjaro..wherever that is.

Kilimanjaro is a mountain in Africa. A bit like Dawn French is in the UK.