Apax Partners, one of Britain's biggest buyout groups, is within days of clinching a deal to sell 10 per cent of itself to sovereign wealth funds from Australia and Singapore and to a Japanese investor.

The Australia Government Future Fund, the Government of Singapore Investment Corporation (GIC) and an undisclosed Japanese firm have agreed in principle to invest several hundred million euros in Apax, according to one senior source.

The deal, which will involve new equity and is still subject to contract, is thought to value Apax at about £1.5 billion. Apax's partners, led by Martin Halusa, have pledged not to sell any of their own equity in the deal.

The new money will be ringfenced and invested in Apax funds. The aim is to replicate the successful arrangement whereby SVG Capital, the listed group, invests largely in funds run by Permira, Apax's UK rival.

Apax has for more than a year been looking for outside investors to help to win it backers in future fund-raisings and to boost its credibility in Asia, which it hopes will be a fruitful market for buyouts in the future.

The credit crunch has dried up the supply of leveraged loans, the fuel for buyout deals, sending the values of private equity houses plunging and making a deal much harder to secure for Apax. Until a few weeks ago, Apax, which has previously been in talks with Middle Eastern investors, regarded a deal as highly unlikely.

Future Fund was set up by Australia's Government to bankroll future pension payments to civil servants. On January 31 it had total assets of A$50.6 billion (£23.3 billion), of which A$37.8 billion was in cash.

Singapore's GIC, chaired by Lee Kuan Yew, the country's former Prime Minister, has been active in investing in Western banks poleaxed by the credit crunch, putting SwFr11 billion (£5.2 billion) into UBS and $6.9 billion (£3.6 billion) into Citigroup. GIC is estimated by Morgan Stanley to be worth as much as $330 billion.

Many of the West's biggest private equity firms, including Blackstone and Carlyle, have recently brought in outside investors. Kohlberg Kravis Roberts last month announced plans to float in New York through a reverse takeover of its Amsterdam-listed investment fund. China Investment Corp's 10 per cent stake in Blackstone has fallen in value by a third.

Apax, based in Jermyn Street, Central London, has been one of Britain's most successful buyout houses, boasting $35 billion under management and recently raising €11 billion for a new European fund. Its investments include the New Look fashion stores and Auto Trader magazine.

Sir Ronald Cohen, Apax's founder, no longer has an interest in it. The biggest shareholders are thought to be the four members of its executive committee, Mr Halusa, John Megrue, Michael Philips and Stephen Grabiner.

Times Recommends

• ‘Lame duck’ fear for FSA as chief quits
• Storm over bailout of EU's most ailing economy
• Northern Rock to drop 100% savings guarantee