LONDON BRIEFING:IT TOOK four years to complete and cost the taxpayer £16 million (€18.6 million). Now, finally, the long-awaited report into the collapse of Britain's last major carmaker, MG Rover, is to be made public, writes FIONA WALSH

The decision to reveal the findings of the investigation follows the news yesterday that no criminal charges are to be brought against the so-called “Phoenix Four” – John Towers, Nick Stephenson, Peter Beale and John Edwards – who ran the company in its final years. They have consistently denied any wrongdoing, although greed is a rather harder charge to defend.

Collectively, they raked in up to £40 million in pay and pensions during their time at the helm and may face moves to bar them from serving as company directors.

In deciding against launching a criminal investigation into the affair, the UK Serious Fraud Office (SFO) has cleared the way for the publication of the report that will detail the demise of what was once one of the proudest names in British manufacturing.

In its heyday in the 1960s, MG Rover employed 250,000 people and produced two in every five cars bought in Britain with famous names such as Wolseley, Austin and Morris.

When the West Midlands firm collapsed into administration in April 2005, just weeks before a general election, it was a bitter blow to Britain’s manufacturing heartland. By then, MG Rover’s share of UK car production had dwindled to below 3 per cent and its workforce slimmed to little more than 6,000. All lost their jobs when the firm collapsed and thousands more were affected at suppliers and local firms dependent on the firm’s Longbridge plant. Creditors were left nursing losses of £1.3 billion.

The collapse came five years after the Phoenix Four bought the business from BMW for a nominal £10, beating an alternative offer from Jon Moulton’s private equity firm, Alchemy Partners.

It was never clear why the SFO was not called in earlier – it was asked to make a decision on criminal proceedings only last month, after inspectors from the department for business handed a copy of the report to business minister Peter Mandelson.

The report is expected to be highly critical of the government’s role in the affair and there were suspicions that, by calling in the SFO, the government was attempting to delay publication until after the next election.

The Phoenix Four have pressed for the release of the report, although it will certainly detail the very generous pay and pension deals they enjoyed even as the company was losing hundreds of millions of pounds.

One of the key questions is whether the business should have been sold to them in the first place when there was a more realistic, but politically less attractive, offer from Alchemy on the table.

Alchemy’s plan would have involved job losses, with Rover production scaled down in favour of the famous MG sports marque.

But those made redundant under an Alchemy deal would have received generous severance packages of some £50,000 and a good proportion of the workforce would have retained their jobs. At the time, however, the unions were critical of the private-equity firm and the government was keen to avoid any major job losses at such a politically sensitive time.

One of the most eagerly awaited parts of the report will be its account of the final days before the administrators were called in.

The government gave the company a £6 million loan to hold off its collapse for a week, a move that has already been criticised by the National Audit Office as “poor value” for taxpayers’ money. The Conservatives described it as little more than an election “bung”.

The report may also shed light on whether, as the Phoenix Four have claimed, the company could have survived had a £100 million government lifeline not been withdrawn at the last minute.

The publication date for the report has been set for September 11th, disappointing those who want it released immediately.

Having waited four years, another four weeks will not make that much difference and Lord Mandelson’s department insisted yesterday that the extra few weeks were needed to contact witnesses and others who were involved in the investigation.

This final delay in publication certainly looks the best option for the minister, who has found himself running the country while prime minister Gordon Brown is away.

A potentially explosive report on the government’s part in the demise of MG Rover is something he is no doubt happy to leave until the boss returns.

• Fiona Walsh writes for the Guardian newspaper in London