Could anyone help, my 64 astra temperture gauge keeps increasing rapidly, first message service due, then turn off a/c due to overheating, then stop and turn off engine due to over heating and alarm starts ringing. Today the gauge does not reset as before. At this point the gauge rapidly goes from max red to 90 and normal? T Few mile later does the same, felt engine when saying overheating and hoses to radiator and not over hot, any suggestions as to the cause, many many thanks in advance.

I would imagine it is the coolant temperature sensor at fault.
This time of year it is quite common for sensors to go faulty with the extreme cold temperatures.

May not flag a fault as it might just come under the 'out of range' category

Run a scan of the engine management system and check live data to see what the sensor is reading