This Carry on film (carry on cabby) was firstly called Call me a cab.
In the scene where Charles Hawtry is training to drive the taxi, it has L plates on. These are real, as after he got the part Hawtry told the producers that he didn't have a driving licence. He had to apply for one and was given a few driving lessons in Pinewood Studios car park to learn the basics for this scene. This is why you don't see him do much taxi driving in the film.