london bus
The runaway red double-decker bus had no driver behind the controls as it careered across a street in Marylebone on 20 August, 2017 Twitter/Turntablist91

Transport bosses are investigating after astonishing footage emerged showing a runaway London bus careering across a main road – with no driver behind the wheel.

The video, taken on a taxi's dashcam, captured the moment the red double-decker runs across three lanes towards a central reservation.

A man believed to be the driver can then be seen rushing to the controls before bringing the vehicle to a stop and reversing it back up a side street.

The incident happened in the early hours of Sunday morning on a street in Marylebone. The footage shows at least one passenger on the bus at the time.

An astonished passenger in the taxi can be heard in the video saying: "What is this guy doing? Is he sleeping? F*****g hell."

The taxi driver responds by saying: "He wasn't in the driving seat... he was asleep."

The black cab driver who posted the footage on Twitter wrote alongside: "Runaway bus ... he got behind the wheel just in time, thank god no casualties."

The Met Police's Cycle Safety Team‏ responded to the video saying it was "unbelievable".

They wrote: "@TfL I suggest would be holding a fully investigation into this matter @metpoliceuk #RTPC."

A Transport for London spokesperson said: "We have asked the bus operator, Go Ahead, to urgently investigate this footage and to report back to us."