All fixed!
Drove for about 30 minutes and seems fine. Temp gauge stays in the middle.
I do however occasionally smell a bit of burning or something but that will probably be down to mystery as the heater isnt on. No steam under the bonnet etc. Charged 81 for 2 hours labour + VAT.
Wasnt the thermostat in the end, was just leaking hoses so the coolant was going elsewhere.
Hopefully it stays good