Which Docor?

Duncan is returning a bag to Harley Street specialist Sir Desmond in his Oldsmobile, when Collier 'borrows' the car to impress a girl and Duncan reports it as stolen. He soon finds the car and drives off but then Paul reports it stolen and calls himself Duncan Waring, to appear to be the rightful owner of the car. They are both arrested and confuse the police by claiming to be the other. Professor Loftus eventually sorts things out by which time Sir Desmond's car has been towed away.