What an extraordinary morning. Almost exactly four years to the day since I pitched up at Boris Johnson’s campaign headquarters with detailed plans for a futuristic, electrically-driven Routemaster, the real thing drove silently on to Trafalgar Square in central London.

Although the ‘New Bus for London’ sticks to Autocar’s mechanical recipe, Northern Ireland’s Wrightbus operation moved the concept on by creating a quick-loading double decker with three doors and two staircases. Design consultancy Heatherwick Studio then came up with the exterior’s super-distinctive glazing and the finely-detailed interior.

Primarily, what makes this bus such a huge leap forward for public transport is the drivetrain and super-rigid aluminium spaceframe body. It’s a range-extender, using a 4.5-litre diesel generator to power and recharged the battery pack. The upshot is that it sails through heavy traffic smoothly (thanks to the electric motors and single-ratio ‘box) and, for much of the time, is running silently on battery power.

Even when the engine/generator kicks in, it is just humming over at 1300rpm. But God is in the details. For example, each passenger on the upper deck gets their own low-voltage downlighter for a calming, ambient, atmosphere.