The prototype, revealed amid great fanfare by London mayor Boris Johnson on Friday, was left on the hard shoulder of the M1 on its way to tests.

Officials admitted the vehicle, the product of a controversial £7.8million scheme to replace the classic Routemasters in London, ran out of diesel.

Commuters saw the double-decker near Dunstable, Bedfordshire, after the driver pulled over to charge the battery.

The hybrid bus’s engine would not restart because the tank was empty.

Labour Greater London Assembly member Murad Qureshi joked on Twitter: ‘Pity Mayor hasn’t installed more electric charging points as his new routemaster conks out.’

Mike Weston, London Buses Operations Director, said the prototype was designed for stop-start driving which recharges its battery automatically.

‘When the bus undertakes long, non-stopping motorway journeys, it can lose charge. The driver is briefed to pull to the side of the road to allow the battery to recharge,’ he added.

‘It was later established that the bus had run out of diesel. Once the bus was refuelled, it carried on its journey.’

Mr Weston added: ‘We will be speaking with the operator to ensure that this does not happen again.’

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