What are the requirements of having vehicles parked in warehouses or business premises? Vehicles catch fire when parked due to faulty electrics but I come across this regularly with the business owners vans parked in workshops, Business owners vintage car parked in a warehouse etc. Garage premises have customers cars in the garage but even these are a risk of fire surely? How would this be dealt with on a fire risk assessment?

The same as any potential ignition source - liklihood of ignition, proximity to other combustibles, effect of a fire on escape, etc, etc. Spontaneous fires in parked vehicles do occur, but are relatively rare and a complete ban is not always necessary or practicable