Thanks Davo, sorted it out last night. I had no flow either way through the small metal pipe inside the expansion tank. It is the internal pipe that the drain pipe attaches to in the expansion tank cap housing and you can't get to it without busting the cap housing or the tank. Dislodged the crud when I hooked up some compressed air to the drain tube pipe and now have clean flow both ways. All back together and running cooler than before so I suspect their has been a slight blockage previously. Car's temp gauge now sits at the first stroke after the blue which is lower than it was previously as it always sat just under the middle stroke in normal driving.
Anyway I am happy with that outcome. Thanks for all that submitted assistance

