Quick history following on from last post:
Had new rad, new water pump, new hoses, etc.....
Another (top) hose split so into a "new recommended garage". The new garage also replaced the pressure cap with a new one, as they said the old one was crap. They also removed an air lock, (burped the system).
The problem I am still having is the temp gauge goes up steadily to near enough 100 and then drops suddenly to about 60 then climbs back up again slowly. This happens all the time whist driving.
The mechanic is muttering about the head gasket.........
Anyone have any ideas - there is now no coolant loss or any leaks.