Tony Blair has intervened in an effort to clinch a vital alliance for car maker MG Rover, it emerged yesterday.

Tony Woodley, general secretary of the Transport & General Workers Union, revealed that the deputy prime minister, John Prescott, had taken a letter from Mr Blair to state-owned Shanghai Automotive Industry Corporation supporting plans for a joint venture with the West Midlands company.

Mr Woodley said he was confident the MG Rover/SAIC tie-up would go ahead. "It's got to go ahead; it's the last chance saloon for Rover."

A spokesman for 10 Downing Street said he could not comment on Mr Blair's correspondence but said: "It is not unusual for the Prime Minister to support British industry."

MG Rover announced last year that it was working on a strategic alliance with SAIC, which also has joint ventures with Volkswagen and General Motors.

The Chinese company has already bought some of MG Rover's technology but the companies are now discussing separate agreements on design and development cooperation and an investment of up to £1bn for new models.

Mr Woodley said MG Rover had done well to "stay in the game" when other car makers had closed or planned to close British plants.

Though SAIC was "the only game in town" as far as MG Rover was concerned, Mr Woodley stressed:

"We should not underestimate the value of this deal to the Chinese." It would bring expertise not only in manufac turing but also in sales and marketing.

Mr Woodley predicted that MG Rover faced " a scary couple of years" until the full impact of the Chinese alliance was felt and that it would help to maintain the current workforce rather than herald expansion.

MG Rover said yesterday talks on forming a joint venture with SAIC were moving forward but it gave no timetable for wrapping up an accord.

"We're making good progress and [holding] a lot of talks with our Chinese partner, but what I can't give you is any kind of firm date to pencil into your diary," an MG Rover spokesman said. Initially Rover had said it hoped to be able to provide details of the alliance early this year.