The Serious Fraud Office is to begin a criminal investigation into the collapse of MG Rover following a four-year government probe into the Birmingham carmaker�s demise, Lord Mandelson is expected to confirm today.

The Serious Fraud Office is to begin a criminal investigation into the collapse of MG Rover following a four-year government probe into the Birmingham carmaker's demise, Lord Mandelson is expected to confirm today.

The Business Secretary is due to make a written statement to Parliament confirming the criminal investiga- tion after a long-running government inquiry into the collapse of MG Rover in 2005, which led to the loss of 6000 jobs at the car plant and many more at suppliers and dealers.

The government inquiry, by inspectors appointed by the Department for Business, was meant to examine what went wrong between Phoenix Venture's acquisition of the firm in 2000 and administrators being brought in five years later.

Part of that investigation was to find out what had happened to more than £400m left to Phoenix Ventures when it took over MG Rover from BMW in 2000.

But the inquiry took far longer than first thought and has cost the taxpayer £16m to produce.

The investigators completed their work last month but the findings are now unlikely to be published in light of the police inquiry.

MG Rover went into administration under insolvency procedures in April 2005, with debts of more than £1bn. Its assets were sold in 2006 to China's Nanjing Automobile, which revived the MG sports car brand.

A quartet of executives known as the Phoenix Four had taken control of the company in May 2000 after originally buying MG Rover for a nominal £10. The business came with an interest-free loan of £427m from BMW, the previous owner. The four executives in charge of MG Rover at the time said then there was "no suggestion of improper conduct".

John Towers, Nick Stephenson, Peter Beale and John Edwards are estimated to have taken out more than £40m in pay and pensions in the years before the business went down.

When the MG plant at Longbridge, Birmingham, closed in 2005 the govern-ment announced a £150m support package for those losing their jobs and for roughly 12,500 workers affected in subsidiary companies.

A spokesperson for the directors defended their actions, saying that "time and again they asked for government help and didn't get it".

A statement on behalf of the directors said: "Four years and £16m of taxpayers' money has been swallowed up on this Department for Business inquiry and the directors' major concern that it will fail to get to the heart of the matter, which is why the government withdrew its offer of a loan to the company at the 11th hour, allowing 6000 workers to lose their jobs."

It added: "Four years on, any suggestion of another further investigation is frankly ridiculous and smacks of kicking this issue into the long grass."

It is understood a decision to call in the SFO could see the publication of the report withheld pending investigation. The Department for Business, Enterprise and Regulatory Reform and the SFO declined to comment ahead of the statement.

Richard Burden, MP for Birmingham Northfield, said: "Like everybody else in the area I have found it incredibly frustrating that we have had to wait so long for this report. The escalating cost of the inquiry has also been a matter of real concern to so many people."