Britain is sounding out private equity buyers for its stake in the Royal Mail Group if it preferred option of a stock market flotation fails, Sky News reported, citing sources close to those advising the coalition government.

The potential sale of the 360-year old group has long been mooted by the government, which has hired several investment banking firms to guide them through the privatization process. Business Secretary Vince Cable has said in the past that the government would like to sell as much as 90 percent of the group while allowing its 160,000-plus staff the option to purchase the remaining 10 percent.

Sky News reported the private equity groups, including CVC Capital Partners, Carlyle Group and Kohlberg Kravis Roberts (KKR), have been "sounded out" by government advisors, but said a private sale would only occur if the government's preferred option of a stock market flotation, which could raise more than £1bn, fell through.

The state-owned delivery group reported a massive £132m increase in first half profits - to £144m - last November in its most recent financial briefing. Group parcel volumes, which account for just under half of its revenues, grew 4.2 percent in the six months ending in September to 673m items.

"Preparations are now underway for the sale of Royal Mail Group," the group said in a statement with the half-year earnings. "Obtaining external capital is a key part of the transformation process as we become a more parcels-focused business and make the investment in technology to do so."

Market speculation has pegged an annoucement on the Royal Mail IPO sometime in the third quarter of this year. However, CEO Moya Greene told Reuters in an interview published in March that a stock market sale isn't likely until at least 2014.