On 11 June 1964 a team from AC Cars met at 4am at the Blue Boar Services (Watford Gap) on the M1. They were there to speed-test a Cobra Coupe GT in preparation for Le Mans.
They didn’t have a long enough stretch of straight test track to check the top speed of the car, so they opted to use a section of the motorway instead. The driver, Jack Sears, registered speeds of 185 mph during the run, which is the highest speed ever recorded on a British motorway. The absence of any speed limit meant their test run was perfectly legal.
Two policemen approached the team at the services afterwards, but only to get a closer look at the car!
A number of car crashes during the foggy autumn of 1965 led the government to hold consultations with the police and the National Road Safety Advisory Council. They concluded that the crashes were caused by vehicles travelling too fast for the conditions.
It was suggested that a speed limit be used during periods when the road was affected by fog, ice or snow, and that an overall maximum speed limit of 70 mph should be tested out. The four-month trial began at midday on 22 December 1965.