The Sunderland plant opened in 1986

At the Detroit Auto show he warned the Wearside plant could lose production of one of its most important cars if the UK continues to stay outside the euro.

The plant makes the mid-sized Almera model, but Nissan says it may make the forthcoming replacement in France.

Now Amicus leaders want "clarification" over the 4,000-worker plant's future.

"Easy" to switch

Regional officer for north-east England, Mel Barras, , said: "Sunderland is the most productive car plant in Europe and Amicus will be seeking to clarify on behalf of our members the points Mr Ghosn has made."

Mr Ghosn said it would be "relatively easy" to switch production to continental Europe.

Nissan's threat to move production of the Almera replacement to France may mean the government steps in with a financial package.

This happened two years ago when it came up with some �40m to keep the Micra supermini model at the Sunderland plant.

Better off outside?

Yet Mr Ghosn, who expressed frustration at what he sees as the government's slow movement on the euro, said production of the Almera replacement would definitely remain on Wearside if the euro was adopted.

Will Mr Ghosn switch production?

"If the UK is in the euro system it is a no-brainer," he told the Financial Times. "We will stay."

Pro-euro campaign group Britain in Europe said Nissan provided "yet another example of how Britain is paying a rising price for staying outside the euro".

"Companies that want to sell throughout the eurozone naturally prefer to insulate themselves from the costs of a volatile pound by basing themselves in a country, such as France, that uses the euro," said Philippe Legrain, the group's chief economist.

No Campaign official Matthew McGregor said: "The UK car industry is doing well outside the euro - both Toyota and General Motors have recently pledged more investment into the UK.

"[Mr] Ghosn seems to be forgetting that the last time we locked currencies in the ERM [exchange rate mechanism], the car industry was decimated and thousands of jobs were lost.

"The best way to ensure our continued success is to keep control of our economy by steering clear of the euro."

Treated 'like robots'

Mr Ghosn's comments come at a time when the Sunderland plant, the largest car production facility in the UK, faces the possibility of its first ever strike.

Members of the Amicus union at the facility have voted to strike in protest at the Japanese firm's plans to transfer its 60-strong purchasing department from Sunderland to Cranfield, Bedfordshire - 200 miles away.

The union complained that the workers were not consulted over the transfer and had been treated like "robots".

But Nissan, which employs 4,000 people in Sunderland, said it had offered an extensive relocation package for those workers who wanted to move.

Management and unions have been holding talks in an effort to avert the strike.

Until now Nissan has enjoyed 18 years of industrial peace at the Wearside factory.