Bob McKenzie oversees the introduction of a third party to the swingometer
Media playback is unsupported on your device

BBC Rewind: Three party swing

The emergence of the Liberals as major players in the general election of February 1974 posed a bit of a problem for the swingometer, which had carved its gilded reputation on representing the swing between the Conservatives and Labour.

Clip taken from Election 74, first broadcast 28 February 1974