A private equity firm is considering buying the Royal Mail stake being put up for sale as part of the government's part-privatisation plans, according to a report yesterday.

CVC Capital Partners is said to be in the early stages of drawing up a potential approach for a minority stake in the postal service, according to the Sunday Telegraph. But the move could attract the ire of trade unions and Labour backbench MPs, which have both voiced opposition to plans to sell a stake in the postal group and who are suspicious of private equity firms and their motives.

The government has already come under pressure, with more than 70 MPs last week backing moves to reject plans to sell a minority stake in the postal group.

The Communication Workers' Union also staged a protest in Westminster calling on Labour to keep the Royal Mail wholly publicly owned.

The government has so far stood firm on the proposals led by Business Secretary Lord Mandelson. Lord Mandelson has stressed there was "no question" of privatising the Royal Mail - but he made clear the government was pressing ahead with its plans.

CVC was not immediately available for comment, but is said to be concerned about any possible backlash if it went ahead with any bid.

However, it has experience in postal services after buying a 22% stake in Post Danmark from the Danish State in 2005, followed by a deal to buy half of Belgian's postal service and last year it announced a merger with Swedish post office Posten.