When Jeff and Marty are sitting in Jeffs car outside the Total garage a Vaxhaull Viva can be see through the passenger window on the forecourt next to the Austin 1800. In the wide shot its not there.
Obvious doubles used for Jeff and Yateman during their fights in the Yateman's office and on the Kershaw's boat.
At 00.36 minutes, when Yateman and his female sidekick pull up on a country road in Jeff's car, studio lights are reflected in the side of the car.
Above Jeff's head when he's talking to Yateman in the office.