The Bentleys are based on the Arnage, but were custom-built in-house by the company’s Mulliner coach building division.
The limos are currently powered by the company’s perennial 373kW/1000Nm 6.7-litre eight-cylinder.
In the Arnage this engine delivers a combined fuel economy figure of 19.5l/100km, but this car is almost 1.5 tonnes lighter than the royal cars.
Bentley says the royal family are big supporters of Crewe’s initiative to switch to biofuels.
It is fully supportive of the move, which means changing over the V8 engines in the cars for a modest fee.
The Queen’s decision follows the lead of the Prince of Wales, who runs his Aston Martin sportscar on old wine while he has converted his Range Rover, Jaguar and Audi to run on discarded cooking oil.
Each of the Queen’s bullet-proof cars is believed to have cost about $14 million each.
One was presented as a gift to her during her Golden Jubilee in 2002.
The second was commissioned by the Crown as a back-up car.
The four-tonne armoured cars are fully maintained by Bentley.
They will not only repel fire from a Kalashnikov AK-47 assault rifle, but protect the occupants from high-powered hand grenades detonated above the roof even if two go off simultaneously underneath the cars.
Like all car makers, the ultra-luxury VW-owned Bentley brand is aiming to reduce emissions and improve economy of its cars.
It has announced that from 2012 it will have flex-fuel engines available across its range.
The company is aiming for a 15 per cent reduction in CO2 emissions by then on all its eight and 12 cylinder engines.
It will also introduce a new powertrain from 2012 that will deliver a 40 per cent fuel economy improvement, while maintaining current levels of performance.
The new engine is tipped to be a hybrid.
When Bentley launched its three-stage environmental strategy early last year, its chief executive, Dr Franz-Josef Paefgen, said biofuels were part of the company’s “corporate social responsibility”.
Technical data reproduced from manufacturer’s websites by permission