Provided you have the proper thermostat installed, you should not need to take any measures to keep the temperature up, but if you do have problems, blanking off the lower one -third of the radiator with a sheet of cardboard should help
Paul Buckley : I do indeed remember radiator muffs . We had one for my Mother's Austin Somerset. Superior beings had remote controlled radiator blinds which operated with drawstrings ; and of course RR had swivelling vertical slats !!