[John Webb]

Triang did car-carrying with their Minic Motorway system. They used an end-loading bay with approach ramp and a bogie wagon fitted with the Minic slot; this was electrified when the wagon was pushed up against the ramp. I believe this was how the original BR system worked - flat trucks with end loading and low guardrails along the edges - but I cannot find any pictures at present. I'll let you know if I do find anything.
Regards,
John Webb

 

[John Webb]

It's interesting - the private companies used covered vehicles and BR went back to open flat trucks as steam locos were removed. Eventually the spread of motorways lead to a reduction in Moto-rail services until it was limited to a small amount carried in vans attached to sleeper trains for Scotland. (Oxford Companion to British Railway History)
Kensington Olympia became the London centre for Moto-Rail traffic, so it may be worth looking at books which give information on that station.
Regards,
John Webb

 

[John Webb]

The old catalogue I've got, and Pat Hammond's history of Triang, show the wagon was long enough for two cars - but quite how you got two cars on without driving one off the far end ....!
Regards,
John Webb