BMC (British Motor Corp.), owners of the Mini, refused to donate any cars for this movie. The chief of Fiat Motors offered to donate all of the cars needed, including Fiat 500s in place of the Minis. Director Peter Collinson decided that, as it was a very British movie, the cars should be British Minis. Fiat still donated scores of cars for filming, as well as the factory grounds. The authorities refused to close the roads, but the Italian Mafia stepped in and shut whole sections of Turin down for filming. The traffic jams in this movie are real, as are people's actions during them.
The silver Aston Martin DB4 thrown off the cliff by a Mafia bulldozer was a fake car. The red Jaguar E-Type (smashed up in the same scene) was restored in the 1990s and featured in a UK classic car magazine. The Lamborghini Miura, which featured in the opening scenes, was recently discovered in a secret car park in Paris and bought by a collector in Wales.
When Charlie Croker gets out of jail, his girlfriend is waiting with a car to drive him home. Charlie sees the flag of Pakistan and mentions that it is the car of the Ambassador of Pakistan. In real life, The High Commissioner of Pakistan owned the car.
The scene between Charlie Croker and the garage owner was entirely improvised by Sir Michael Caine and John Clive.
Peter Collinson: When the Minis are being driven onto the coach after the heist, he is standing at the doorway guiding the cars in.