It is normal for the temperature gauge to sit just below horizontal. "About half past 8" is correct.
When pushing on, and putting a lot of heat into the turbos, this heat is transferred via the oil and water to the engine's cooling system - it's pretty good, about 10-15 minutes on track is about when I expect the temperature gauge to creep up. I know Lucas did both short and long journeys, and drove it like it was designed to be and like a granny, and didn't have any overheating issues with it (otherwise he'd have likely been on the phone to me asking for some help!) - and I didn't experience that when I borrowed it, either, so it's surprising to hear you've had this so soon :(
The dash temperature gauge is fed via
this sensor - for the sake of £7.50 (at current price) I'd be tempted to change it and see if the problem remains.