A flying taxi business owned by the billionaire boss of Ovo Energy has warned it will run out of cash by next September.

Vertical Aerospace, founded by Stephen Fitzpatrick, is scrambling to raise funds after one of its aircraft crashed during a test flight in the Cotswolds four months ago.

Concerns over the Bristol-based start-up’s future were raised in a recent letter to shareholders, as Mr Fitzpatrick said the current cash runway” will take it “towards the end of Q3 2024”.

This has since been followed up with a further warning that says “dependency on raising additional capital indicates that a material uncertainty exists that may cast significant doubt” over its ability to continue as a going concern.

Vertical Aerospace, which is producing a five-seater flying taxi that can reach speeds of up to 200mph, also said that it “may need to scale back investments” if the group is unable to raise cash by mid-2024.

So far this year the company has racked up ￡42m of losses, down from ￡135m posted for the same period last year.

Mr Fitzpatrick has incorporated Vertical Aerospace into his sprawling business empire, the bulk of which is made of Ovo Energy, Britain’s fourth-largest gas and electricity supplier that serves 4m customers.

He has also recently bought Kensington Roof Gardens, a party venue in west London, once owned by Sir Richard Branson, that he wants to turn into an exclusive private members’ club.

Vertical Aerospace was launched by Mr Fitzpatrick in 2016 and listed on the New York Stock Exchange two years ago, although it has been registered in the Cayman Islands.

Its share price has fallen by 97pc since its float and it is now valued at around ￡168m, down from an initial valuation of ￡1.74bn.

Michael Cervenka, the chief technology officer, has likened the company’s growth story to that of Elon Musk’s Tesla.

Despite warnings over its finances, Vertical Aerospace has said it is “working on plans for a high-profile public flight featuring an iconic UK landmark”. It is also planning to land one of its aircraft at Heathrow Airport.

The company’s flying taxi takes off vertically like a helicopter before tilting its engines forward to act more like a regular plane.

It was granted design approval by the Civil Aviation Authority, which the company hailed as a “critical step forward”.

Vertical Aerospace was contacted for comment.