I rang RPI Engineering this morning and told him my woes.
He said he has had the same conversation many times with Plus 8, TVR, RV8, Disco and Range Rover owners of the same vintage.
Basically it is an ignition issue. He is going to email me with the details of their cure, which involves the Tornado chip, coil, IAM, and some other things I can’t remember.
So, I am going to leave it till the new year when I can book in for the work, which apparently takes five hours but they like to have the car for a couple of days.
I had a good drive today, and it was great. Stalled a few times but I can live with that now that I can see the way out.

Thank you all for your help, ideas and support.
Looks like we may have a couple of days on the Norfolk Broads in the new year.
Take care, stay safe and have a great Christmas and new year.
Phil