The new 'greener' Prius that you can plug in to any power socket

Drivers will be able to drive up to six miles on electric power only and emissions-free - sufficient for most commuting journeys.

The plug-in Prius can be charged from any domestic socket, giving it a far greater range under electric power than the current model that relies solely on its petrol engine to charge its batteries.

Greener and quieter: A new Toyota Prius charges up at a power socket in the City of Westminster as part of trials being undertaken in London

When running on electricity, the car is near silent, produces no emissions, and uses no fuel.

It takes between one and a half to two hours to fully charge - and then tops itself up while being driven.

But like the existing Prius it still has a fuel tank - and is still capable of switching, automatically, between its 1.5 litre petrol engine and electric motors.

It has a top speed of 105mph and can accelerate from rest to 62mph in 10.9 seconds.

Energy company EDF - which has installed charging points around the UK and which part-funded new sockets in Westminster - says it is the next step to breaking the tyranny of rising fuel prices.

The first plug-in Prius, which also has additional battery capacity, will undergo rigorous testing in London as part of the power company's fleet before Toyota decides when to make the car available to the public.

The prototype has proved even 'greener' than the standard model in early tests.

Unlike the current £7,282 Prius, bought by around 25,000 motorists in the UK, the Plug-in Hybrid can be driven as a purely electric vehicle for short journeys.

According to EDF, the extra charge that the batteries receive when the car is plugged in enables the car to use 60 per cent less petrol on journeys of up to 15 miles.

To further extend the number of miles the car can travel on its batteries, EDF plans to make charging points more accessible on public roads and at car parks.

It has already installed 40 charging posts in the UK and says it will install a further 100 across London.

A Toyota spokesman said: 'Early test results indicate that fuel efficiency is  significantly higher than the current Prius.'

'It is the best of both worlds,' said an EDF spokesman.

'It enhances the benefits of hybrid technology while avoiding the constraints traditionally linked with electric vehicles.'

Business Secretary John Hutton, who was helping unveil the new prototype in London today, said: 'I welcome the launch of this trial here in the UK.

'I am pleased to see industry pulling together to work on diversifying energy use and cutting global car emissions.

'We hope that this trial will provide an invaluable insight into the future development of UK electric and plug-in hybrid vehicles.

'It leads us one step closer to making a reality our ambition of becoming the  number one location for low carbon vehicles.'

The trial will last for a year and help offset negative publicity following the claim that nickel for the car's battery is produced at a Canadian factory whose sulphur dioxide fumes have destroyed vegetation in surrounding countryside.