Silverstone racing circuit straddles the border of Northamptonshire and what other English county?

Silverstone Circuit is a motor racing circuit in England, near the Northamptonshire villages of Silverstone and Whittlebury. It is the current home of the British Grand Prix, which it first hosted as the 1948 British Grand Prix. The 1950 British Grand Prix at Silverstone was the first race in the newly created World Championship of Drivers. The race rotated between Silverstone, Aintree and Brands Hatch from 1955 to 1986, but settled permanently at the Silverstone track in 1987. The circuit also hosts the British round of the MotoGP series.

The circuit straddles the Northamptonshire and Buckinghamshire border and is accessed from the nearby A43. The Northamptonshire towns of Towcester and Brackley and Buckinghamshire town of Buckingham are close by, and the nearest large towns are Northampton and Milton Keynes.

The Silverstone circuit is on the site of a World War II Royal Air Force bomber station, RAF Silverstone, which opened in 1943. The station was the base for No. 17 Operational Training Unit. The airfield's three runways, in classic WWII triangle format, lie within the outline of the present track.