The circuit opened in 1927 and the first race, for motorcycles, was on 21 May 1927. The circuit was 1-mile (1.6 km) long, and ran on pre-existing paths through the park, including an infield loop past the lake. The surface had tarmac-covered bends, but the straights only had hard-packed gravel. Improvements begun in December 1936 increased the circuit to 2 miles (3 km), and tarmac covered the entire length. 20 cars entered the first London Grand Prix on 17 July 1937, a race eventually won by Prince Bira in his ERA R2B Romulus at an average speed of 56.5 mph (90.9 km/h). Later that year, during the International Imperial Trophy meeting also won by Bira, the BBC broadcast the first ever televised motor racing. With the outbreak of World War II, the park was taken over by the Ministry of Defence, and it would not be until 1953 that race meetings could take place again. The circuit had been reduced in length to 1.39 miles (2.2 km), bypassing the loop past the lake, and pressure from the local residents led to an injunction which reduced motor sport events in the park to only five days per year. A variety of races took place, including sports cars, Formula Three, the London Trophy for Formula Two, and non-championship Formula One races. Average speeds continued to rise over the years, with the first 100 mph (161 km/h) lap average set in 1970 by that year's Formula One world champion, Jochen Rindt. Also in 1970, the injunction limiting race days expired and racing was increased to 14 days a year. However, driver safety was coming into focus in the early seventies and it became clear that racing around a park at 100 mph (161 km/h) was not safe. Expensive improvements were undertaken, but it was not enough to save the circuit. The last International meeting was in May 1972, the final lap record going to Mike Hailwood at an average speed of 103.39 mph (166.39 km/h). The final meeting was held on 23 September 1972, but club events still continued until the circuit's final closure in 1974.