Theoretically every car used on UK roads has to be taken to a VCA testing station, in order that it can be inspected and then issued with a certificate confirming that it complies with the requirements of the Vehicle Construction and Use Regulations.
However the system permits manufacturers to seek, and obtain, 'type approval' for each of their models. That means that only a single car has to be examined and then all other cars with the same specification will be deemed to comply with the Regulations.
Any car which differs from the manufacturer's standard UK model (in respect of anything covered by the Regulations) still needs to be submitted for individual approval. Approval will not be granted for any vehicle which does not comply with the Regulations and using that vehicle on a public road will be a criminal offence.
I used to be a 'trade plater'. One of my jobs was to collect imported new vehicles (with non-UK specifications) from Felixstowe Docks. Those vehicles had to be immediately taken to the nearest testing station (in Norwich), as driving them anywhere else would have been illegal. The vehicles had speedometers only displaying km/h. I mentioned this to one of the testers who stated that the vehicles would not be released from the testing station, with a certificate of approval, until the importer had arranged for speedometers displaying mph to be fitted.
Chris