The owners of Rolls-Royce have said the car will be built overseas if it fails to win permission for a factory in Sussex.
The warning came as councillors in Chichester prepare to decide if a car manufacturing plant and administrative headquarters can be built in the heart of the countryside.
The £60 million plan would see 1,000 cars a year coming off the production line, creating more than 400 jobs.
Friday's meeting of the district development control committee is being recommended to approve the scheme for a site at Goodwood.
But the proposal will also have to go before the full council and be referred to Environment Secretary John Prescott.
German firm BMW, which owns Rolls-Royce, said the factory and offices have been designed to blend into an area of countryside where new development is usually banned.
The company told the council: "There is a pressing need to develop a state-of-the-art building on a private, secure site if the future of Rolls- Royce production is to be assured.
"If a suitable location is not found and development does not proceed, BMW will be forced to take this essentially British product abroad.
"It is the intention behind the current planning application for the manufacturing and head office proposal at Goodwood to ensure Rolls-Royce remains in the UK."
BMW said sinking the factory into a site where gravel had been extracted and giving it a green roof would avoid creating an eyesore.
It said the plant would be worth more than £14 million a year to the West Sussex economy.
The site is owned by Lord March's Goodwood estate and cars would be tested on his motor racing circuit which is close to the factory site.
Councillors have been told of 66 individual objections to the scheme. Many people have complained a green field site was being used when brownfield ones were available.
The plan has also come under fire from the Council for the Protection of Rural England which believes permission would "destroy the credibility" of policies designed to protect the countryside.
It said the need for jobs should not be allowed to tip the verdict in favour of BMW because brownfield sites were available.
A report from council planning officers acknowledges a conflict with countryside policies but says the employment opportunities also carry "considerable weight".
Dealing with fears of more cars on country lanes in and around Goodwood, the council will tell BMW it must pay £210,000 towards improving bus routes in the area as well as providing better footpaths and a cycle path.
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