Took the thermostat out yesterday to see if that changed anything. Drove 20 miles of dual carriageway at 85 degrees and 10 minutes in slow town conditions where the temperature rose to 95 degrees, then another 20 miles of back lanes to Topcats. Car didn't miss a beat and the temperature seemed fine.

I'll leave it with Topcats for a few days (and a few minor jobs) and they'll drain, flush and correctly refill to cooling system - Warren did mention a high flow thermostat they fit to the TVRs as mine seems to be working ok with no thermostat.

Fingers crossed things will be sorted for this weekend !

Thanks for info/ideas guys