The disclosure will bring more embarrassment to ministers; there have been repeated allegations of businesses making a killing on former nationalised companies which have been sold off cheaply.
The public-finance watchdog is looking into the sale of Porterbrook Leasing as part of a wider investigation into the privatisation of all three former British Rail rolling- stock companies. Labour has claimed that their sale by the Department of Transport allowed taxpayers to be "ripped off."
Porterbrook was bought by its management for pounds 527m in January last year and was sold to Stagecoach seven months later for pounds 825m. The sale netted pounds 36m profit for the company's managing director, Sandy Anderson, a former British Rail terminal manager. In total, he and three other managers made pounds 70m, while the remaining 44 staff each made an average profit of pounds 390,000.
The National Audit Office (NAO) report, expected in the spring, is likely to call into question the amounts raised not just from Porterbrook but the sale of the two other rolling-stock companies, Angel Train Contracts and Eversholt Leasing.
A NAO spokeswoman confirmed it was preparing a report into the sale of the three companies but refused to comment on likely conclusions or the timing of its publication. The report is expected to include a separate section on the sale of Porterbrook. The original purchase of Porterbrook was funded with pounds 75m equity and pounds 352m debt. Stagecoach paid pounds 475m for the equity and injected pounds 350m of debt.
This meant the Porterbrook management and their City backers, led by the investment bank Charterhouse Development Capital, netted pounds 400m profit on their shares.
The management and employees had 20 per cent of the equity, realising pounds 80m, and City institutions made pounds 320m. Apart from Mr Anderson, the other big gainers were Porterbrook's finance director, Ray Cork, who made pounds 17m, engineering director Tim Gilbert, who netted pounds 11m and chairman Peter Watson, whose shareholding was worth pounds 4.75m. Mr Watson is also chief executive of another recently privatised company, AEA Technology.
The Porterbrook sale to Stagecoach has cast doubt on whether the other two companies were also sold too cheaply. Eversholt Leasing was sold for pounds 580m to a management and employee buy-out. The consortium paid pounds 70m for the equity, with 15 per cent of the shares going to managers and staff.
The third company, Angel Train Contracts, was sold for pounds 700m to a consortium led by the Japanese investment bank Nomura, supported by John Prideaux, a former BR executive who once ran InterCity. Nomura has made no secret of its desire to sell Angel or merge it with a train-operating company like Stagecoach.
Eversholt Leasing is also a potential bid target, in which case its 60 employees, led by the former Hanson executive Peter Harper, will be sitting on multi-million bonanzas.
In a report last October on the sale of the first three passenger rail franchises - Great Western Trains, the London-Tilbury-Southend Line and South West Trains - the NAO criticised the Government for ignoring the advice of its own franchising director and failing to include clawback provisions so that taxpayers could share in abnormally high profits.