A life-size mock-up of the new hop-on, hop-off double-decker bus for London was unveiled today by the capital's Mayor Boris Johnson.

Showing off the bus at Acton in west London, Mr Johnson said he was looking forward to the first of the buses coming into service in 2012.

The new bus is based on the old driver-and-conductor red Routemaster which was withdrawn from regular service in 2005 although some still run on popular tourist routes in London.

The new bus is being designed by Thomas Heatherwick and built by Northern Ireland-based Wrightbus and will be 15% more fuel efficient than existing hybrid buses, 40% more efficient than conventional diesel double-deckers and much quieter on the streets.

The pioneering design makes use of lightweight materials, with glass highlighting key features and producing a light and airy feel inside the bus.

As with the Routemaster, the new bus has an open platform to provide a hop-on, hop-off service.

Details of the design of the bus were first announced in May.

Braving the wind and rain at Acton today, Mr Johnson said: "Standing on the rear platform of this delectable bus brings back a sense of nostalgia but conversely also demonstrates the quintessence of the latest technology and design, making this bus fit for the 21st century.

"It is wonderful to see those two-dimensional designs we unveiled in May have been forged into this amazing bus and I cannot wait to be launching the buses when they first enter public service in 2012."

Mark Nodder, managing director of Wrightbus parent company Wright Group, said it was "a real thrill" to see the bus come to life.

Mr Johnson said: "This is a fantastic machine. There will be a substantial number on London's roads and there is already a lot of interest from around the world for this bus."

Mr Johnson was determined to bring back some form of the Routemaster when he took over as Mayor.

London Transport Commissioner Peter Hendy said at Acton today: "There have been some who have said this bus is some form of vanity project. That's simply not true."

The bus has three doors and two staircases, with the jump-on, jump-off platform able to be closed at quieter times, such as in the evenings.

Meanwhile, another set of the ultra-long "bendy buses" will cease to operate from this Saturday when route 18 in London will be "debendified" and conventional double-deckers will take over.

All bendy buses will be gone by the end of next year.