The new bus to take London streets has been finally unveiled In Northern Ireland, where it has been manufactured.

Formerly described as a "21^st century Routemaster," the new bus is the first designed specifically for the streets of London in more than 50 years and it has been built by engineers at the Wrightbus factory in Ballymena, a company that already supplies many of the capital's 7,500 buses.

"This fantastic machine is chock full with the latest technology and London buses will be world leaders once again when the first eight buses take to our roads early next year," said mayor Boris Johnson.

"Our new bus is an improvement on standard double decks in every respect and has been designed with this city and its wonderful population in mind. It showcases the very best of British manufacturing and design and simply oozes with quality," he added.

The new bus incorporates hybrid technology and will be the most environmentally friendly bus of its class. Under test conditions the vehicle achieved fuel consumption of 11.6 miles per gallon which compares to 8.6mpg for a hybrid bus and 5.8mpg for a normal diesel bus. The vehicle is also expected to be the quietest of its kind.

According to the mayor's office, if the entire fleet of London buses were based on the new buses, CO2 emissions in the capital would be reduced by 230,000 tonnes a year.

Like the iconic Routemaster, the new bus has a rear open platform that allows passengers to get on and off as they please. It also has two sets of staircases.

The bus is expected to carry two crew members between 7am and 9pm - a contemporary version of a conductor.

The project has been criticised by the Tory mayor's Labour opponents as a costly investment.

The prototype will arrive to London in December in preparation for entering full service next year. It is expected to be carrying passengers by February 2012.