CLOSELY guarded off-road prototype plans of Wiltshire's first electric car have been released by Dyson.

The company revealed the patent plans - which have been kept secret since they were submitted 18 months ago - for the unnamed electric car, which will be entirely designed and tested at the Hullavington Airfield in Wiltshire near Junction 17.

After investing £200 million in facilities the firm will construct the vehicles to begin the latest phase of testing next month.

The cars will however be manufactured in Singapore.

In a letter sent to 500 staff, the company's founder Sir James Dyson said the car will contain “fundamentally new technologies and make some inventive leaps" by developing the car "from the bottom up".

A number of patents for new cars have been issued, although the drawings “don’t reveal what the vehicle will really look like or what it will do", he said, as he called on staff to keep key details secret.

The plans do reveal advances made in the aerodynamics, efficiency and vehicle architecture of the car, he added.

Patents for the prototype detail ways to lengthen the battery life of the car and highlight an intention to use “very large wheels, giving a low rolling resistance and high ground ” to suit bumpy terrain as well as to improve “range and efficiency”.

Drivers might also have to adopt a more reclined position to allow for a lower cabin height and shallow windscreen angle to reduce drag and therefore improve driving range further.

The inventor behind brightly coloured manoeuvrable vacuum cleaners and more efficient hand dryers is on the front foot ahead of plans to phase out petrol cars.

The government announced in 2017 that it plans to phase out the sale of new petrol or diesel vehicles without hybrid technology by 2040, although Sir James has called for this deadline to be brought forward.

Dyson has set aside around £2.5 billion to invest in the project, as it leaps into the highly-competitive electric car market alongside the likes of Elon Musk’s Tesla.

The car is set to be manufactured in Singapore, the new home of Dyson’s corporate headquarters after the controversial decision to move the HQ this year.

The Brexit-supporting billionaire inventor faced fierce criticism after he revealed plans to relocate its head office from Wiltshire to east Asia.

The company is set to start work on its plant in Singapore, ready for a launch date set for 2021.