Leading investors in a British company developing the engine for a futuristic space vehicle dubbed the new Concorde have significantly written down the value of their stakes in the business.

Artemis has cut the value of its 2.3 per cent holding in Reaction Engines by 75 per cent, a move that comes after a 25 per cent writedown made in July. Artemis Alpha Trust, the fund that manages the London-based fund manager’s stake, now values it at £1.2 million, compared with £6.4 million in April.

“Although the company has achieved significant progress in commercialising its innovative technology, recent revenue growth has been slower than anticipated,” the fund told its shareholders. “The company is currently pursuing an internally led fundraising that is likely to be at a discount to the last valuation.”

This week Schroders Capital Global Innovation Trust lowered the value of its investment in Reaction Engines from £10.6 million at the end of last year to £1.4 million as of the end of June. The lower valuations suggest that Reaction, whose shareholders also include BAE Systems and Rolls-Royce Holdings, is now worth roughly £34 million.

The Schroders trust said that despite steps by the company to commercialise its heat exchanger technology and recent contract awards, revenue growth had been slower than expected.

Schroders inherited its stake from an investment originally made in 2018 by Neil Woodford, 64, the fund manager who presided over one of Britain’s worst investment scandals. The trust took over running Woodford’s failed fund, the Woodford Patient Capital Trust, which was one of Reaction’s early backers.

The engineer, which was founded in 1989, is chaired by Philip Dunne, 66, who was a Conservative defence minister from 2012 to 2016. The company has been led by Mark Thomas, 53, since 2015. He joined after a 25-year career at Rolls-Royce, the aerospace engine maker.

Reaction Engines has been developing a hybrid jet and rocket engine, known as Sabre, with ambitions to power hypersonic space vehicles capable of travelling at speeds of up to 19,000mph. Key to its development is the company’s pre-cooling technology that prevents engines from overheating.

Rolls-Royce backed the company with a reported £20 million in 2020 after joining forces with Virgin Galactic on a project to develop a supersonic business jet that would cut a journey from London to New York to 90 minutes. Last year the company raised £40 million of additional equity, taking its total funding to £150 million.

Reaction Engines was approached for comment. Artemis declined to comment.