Temperature gauge jumps off the scale when driving

[Chambers87]

Hi there, just picked up a 2002 Jaguar XKR, 62k miles, great history, well kept car. Have driven around 300 miles so far and the only thing that has caused issue is the temperature gauge instantly jumping to the high end whilst driving. The engine management light comes on and ‘low performance mode’ engages and the car limps along. Of course the first time it happened I stopped right away, worried to what I find under the bonnet but there is no sign of overheating, no leaks, coolant remains at same level, no water in the Oil etc. after leaving 10:15 mins the car starts up and all is normal, no lights, gauge in the normal band. I am guessing a sensor of some sort is out perhaps, has anyone had anything similar and could point me in the right direction, my local jag specialist is booked out until October so would like to try and rectify this before then. 
 

many thanks for any help or advice.