The Serious Fraud Office (SFO) is to investigate the collapse of MG Rover after a four-year probe into the Midlands carmaker's demise, it was reported today.

Business Secretary Lord Mandelson is expected to confirm the SFO's involvement tomorrow when he makes a written statement to Parliament.

The move comes after a long-running inquiry into the collapse of Birmingham-based MG Rover in 2005, which led to the loss of 6,000 jobs at the carmaker and many more at affected suppliers and dealers.

The four executives in charge of MG Rover at the time reportedly said then there was "no suggestion of improper conduct".

The Government launched an investigation immediately after Rover's collapse to examine what went wrong between Phoenix Venture's acquisition of the firm in 2000 and administrators being brought in.

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

The report was finally submitted around three weeks ago and there were calls last month for the findings to be made public.

However, it is understood a decision to call in the SFO could see the publication of the report withheld pending the investigation.

The Department for Business, Enterprise and Regulatory Reform (BERR) declined to comment ahead of the statement tomorrow. The SFO also declined to comment.

The MP for Birmingham Northfield, Richard Burden, whose constituency includes almost all of the former MG Rover site, last month expressed frustration at the length of the report and urged an imminent publication of the results.

He 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, including me."

The inquiry was set up under the Companies Act by then trade and industry secretary Alan Johnson.

Mr Johnson said at the time an investigation covering the two years leading up to the collapse was in the public interest.