Goldman Sachs, which is running the sale of the unit, has given bidders less than three weeks to submit indicative offers as confidential material was only dispatched on Sept. 13, three sources said.

Prospective suitors for the business, which is called Old Mutual Global Investors (OMGI) and sits within Old Mutual Wealth, include private equity funds TA Associates and Hellman & Friedman, according to one of the sources, who added that a host of buyout firms had been invited to run the rule over the unit.

Old Mutual is aiming for a price tag of at least 500 million pounds, one of the other sources said. The company declined to comment.

Buxton is one of Britain's star fund managers and joined OMGI from Schroders four years ago, first as head of UK equities before being promoted to chief executive of the business in 2015.

The decision to examine a deal for OMGI comes as Anglo-South African insurer and financial services giant Old Mutual presses ahead with an ambitious broader plan to break itself into four separate companies, one of which is Old Mutual Wealth. It plans to list the wealth business on the stock market next year.

Old Mutual Wealth said on Sept. 2 that, as part of its plans for a float, it was overhauling its funds arm and that it considered multi-asset investment to be "core", with Paul Simpson appointed to run that business.

Meanwhile, OMGI will focus on single strategy investing under Buxton. Old Mutual Wealth said it would work with OMGI's management to examine "internal and external structures".

A source told Reuters earlier this month Buxton was eager to strike off on his own and had been in talks with private equity firm TA Associates about a possible management buyout of OMGI.

The TA Associates' approach spurred Old Mutual to hire Goldman Sachs to run a formal sales process for the Buxton business, the source said.

(Reporting by Ben Martin and Pamela Barbaglia; Editing by Susan Fenton)

By Ben Martin and Pamela Barbaglia