[BAracer]

The South Manchester Slot Racing Club Classic Mini Rule Set (courtesy of Angelo Amato)
A 'Metro 6R4' Rule Set

And a slightly modified Nonfractal TR7 Rule Set...
Scalextric Metro body. No chopping the roof off (making it into a cabrio)
48mm or 54mm max track (tba)
Any chassis and side skirts from any material.
Any weight can be added internally to the car.
Any interior (but there must be an interior with a discernible driver with full head/helmet.
Four wheels are mandatory, all four with face detail or inserts.
No magnetraction magnets
No rare earth motors 
Car must have transparent windows 
Suspension is permitted 
Guide must not protrude beyond the front of the car when viewed from above.