The Ministry of Defence is poised to drop a Rolls-Royce engine in favour of an American alternative, potentially jeopardising 200 jobs at Rolls-Royce in Patchway.

It is claimed defence officials were preparing to reject the jump-jet version of the Joint Strike Fighter, which uses a UK-built Rolls-Royce engine.

They were planning to opt instead for the conventional model, or "CV" variant, to use on its two new aircraft carriers.

About 200 of the 3,500-strong workforce at Rolls-Royce in Patchway work on the JSF project.

The move could also jeopardise 750 jobs at the Derby base of Rolls-Royce.

The claimed move, welcomed by many defence analysts and the Royal Navy, will mean that the MoD has wasted £500 million of taxpayers' money paid to Rolls-Royce to develop the highly complex engine to allow vertical take-off similar to the Harrier jump jet.

A domestic row is also brewing as Rolls-Royce was not widely consulted on the forthcoming decision, which is expected to be announced in the autumn, according to reports.

The company said it regarded the story as "speculation" and would not comment any further.

But the company faces job losses with up to £5 billion in lost revenue in engine sales if the MoD rejects the "B" version of JSF fighters and goes for the "CV" conventional model which takes off from an aircraft carrier runway.

But the MoDe insisted that no decisions had been taken and that the jump-jet version, or Short Take Off and Vertical Landing (STOVL), remained its "preferred solution".

A spokeswoman said the new carriers were being built to an "adaptable design" that could operate both kinds of fighters.

"The QE Class are designed around the operation of the STOVL Joint Strike Fighter aircraft, and this remains our preferred solution to meet the UK's Carrier Strike requirement along with the Queen Elizabeth Class of carriers and the Maritime Airborne Surveillance Capability," she said.

Quentin Davies, the procurement minister, said: "We have to take an immensely important decision.

"The testing and evaluation phase has been ongoing of the first three aircraft. We have to take a decision as to which version of aircraft we shall be agreeing and we shall be focusing on this situation in the coming months."

The Navy has been flying Harrier jump jets off carriers for more than three decades and it is believed the "B" variant was originally chosen as a continuation of this when the Harrier goes out of service in 2015.