When Brian and Laura stop the Porsche, the driver states that the car was new and had only "12 miles on the clock." After Laura steals the Porsche, a close-up of the odometer clearly reads that the car has 754 miles "on the clock."
The headrests in Gwenda's car disappear then reappear between shots as she is leaving the railway station.
When Brian convinces Pat to take over driving she is apprehensive at having to drive on the left, explaining she's lived in Australia for the last 20 years, however Australia also drives on the left.
By the end of the movie when Stimpson is delivering his speech and the left-arm coat-sleeve falls down, it's obvious that John Cleese himself pulls something with his right hand, making the sleeve fall.