One off Scalextric car ( aero engine )

I was given this over 40 years ago and from what I was told by the owner was that this was a car he had made for Scalextric as a one off prototype. The genteleman who gave it to me was an engineer and a very keen aero modelling enthusiast. He also gave me a fairly large collection of engines.
He built it for a straight track and as you can see it has a petrol engine. It also comes with another hand made metal body.
It is a really nice piece of engineering and I have no idea of what it is worth as it has no providence
I did email the company ( Scalextric ) but never heard back from them.
I cannot see the make of the engine or size---I would say a .75