Well - I posted the other day re my water pump falure and subsequent refitting and then overheating problems.
I drained the coolant again today and re-filled using the Haynes Manual Method (fill up via heater inlet hose and then via header tank, run engine until warm and then keep an eye on header tank) still overheating. The heater hose that runs across the front of the engine got warm but the radiator hoses remained cool. I decided it must be the thermostat - unlikely, but worth a try.
I got a new thermostat and fitted it and thgen filled the system using Tim's advice, fast tickover, very slow fill via header tank. I thought it was better but no, when I took it out it started to overheat again. When I got back I ran the engine in its hot state (it only gets in the red when under load) and felt the rad pipes. The one on the side nearest the thermostat was stone cold, the one the other side was a bit warm but the radiator was stone cold. It seems there is no flow at all - any ideas on what I am doing wrong here? - Could it be a blocked radiator core?