Trade and Industry Secretary Alan Johnson will come under intense pressure this week to launch a full-blown government inquiry into the collapse of MG Rover and the role played by its directors, known as the 'Phoenix Four'.

Whitehall sources indicate that a preliminary report into the company's accounts carried out by Sir Bryan Nicholson, chairman of the Financial Reporting Council, will point to a list of unanswered questions.

Officials in DTI are considering whether to launch a full-scale inquiry under either section 432 of the Companies Act, which would lead to appointing external inspectors, or an internal investigation under section 447. The conclusions of the Nicholson inquiry will be a key factor in their decision.

There is frustration that the inquiry, launched on 15 April in the heat of the general election campaign, has not had time to complete a thorough investigation of the complex web of MG Rover companies and has been hamstrung by its narrow remit, allowing it only to check the accuracy of published accounts.

The report, carried out by an FRC subsidiary called the Financial Reporting Review Panel, concludes that serious issues need further investigation. These are thought to centre on why the profitable assets of the company were separated from the loss-making ones, along with some property transactions.

A senior Whitehall source said: 'There are issues that require further investigation before we can come to a view as to whether there were irregularities or not.'

Asked whether a DTI inquiry was likely, the source added: 'I think, given the profile of all this, it would be worth having a further look. Officials in the department are already thinking very hard about a further inquiry.'

The Nicholson inquiry was launched by Johnson's predecessor, Patricia Hewitt, after Rover was put into administration in early April amid allegations that more than £400m were unaccounted for in the company accounts.

Sources indicate that the five weeks the FRRP has spent looking at the accounts of MG Rover, its parent Phoenix Venture Holdings and other of the more than 20 other companies in the group, has not been enough.

Johnson will face pressure from MPs and unions including Amicus and the Transport & General Workers Union to publish the report. Roger Maddison of Amicus said: 'We called for the investigation. We want the report to be published.'

A DTI spokeswoman said she would not pre-empt the findings of the FRRP report, but added that a further inquiry was an option that would be considered by Johnson when he received it.

Meanwhile, administrator PWC says it believes SAIC's claim to have exclusive rights to make Rover models and engines can be challenged, and that there is still interest from several parties in buying all or part of the business.