Which UK motorway is the London orbital road?

The UK motorway known as London’s orbital road is the M25 motorway.

The M25, officially also called the London Orbital Motorway, forms a broad ring around most of Greater London. At about 117 miles, or 188 kilometres, it passes through or near several counties and provides links to major routes including the M1, M4, M3, M20 and M11.

Construction grew out of post-war plans for several concentric London ring roads. The first M25 sections opened in 1975, and the complete orbital route was officially opened on 29 October 1986 by Prime Minister Margaret Thatcher.

Strictly speaking, the M25 does not itself complete the entire circle. The eastern gap across the River Thames is closed by the Dartford Crossing, designated the A282 rather than a motorway. That technical detail does not change the standard quiz answer: the M25 is London’s orbital motorway.