Martin Currie, the specialist investment manager, yesterday moved to ensure its independence when it concluded a deal to bring in two external investors.

New York-based investment firm Crestview Partners and investment vehicles associated with Lord Jacob Rothschild have been invited to buy in to the Edinburgh-based investment house as junior partners in a deal that will see Martin Currie's employees continue to control 75.1% of the firm.

The investment sees 17.43% of Martin Currie's equity sold to Crestview Partners and 7.47% to interests associated with Lord Rothschild.

The boutique investment house has been reviewing a number of options over the past year for generating additional funds - including a partial flotation - to drive its strategic plan. The aim is to double the size of the £14.4bn business over the next three years, and grow its presence in the US wealth management market.

Martin Currie chief executive Willie Watt said: "We looked at a listing but we decided it was not a road we wanted to go down."

Instead, the company opted for investors of a like mind, with a view to establishing a closer relationship, rather than inviting in a raft of faceless shareholders, he said.

Watt added: "Independence and employee ownership have been distinguishing features of Martin Currie since its beginnings in 1881. They allow us to attract and retain people who excel at what they do. They enable us to make long-term decisions, such as almost doubling the size of our investment team over the past five years, or closing products to new investors in order to protect performance.

"But as the business succeeds and the share price rises, it becomes harder to buy out retirees, and harder for newer staff to be able to afford the conversion of options into shares.

"So that is one reason for arranging this strategic investment. It provides the limited liquidity we need, and facilitates the orderly transfer of ownership from one generation of employees to the next.

"By exercising options, as part of this transaction, 26 of our key investment personnel and more recent recruits will become larger shareholders in the business. This is a strong vote of confidence, both in the transaction itself and in Martin Currie's future.

"The second reason is that the parties making this investment bring extensive experience, contacts and standing in our field.

"For these reasons, I am certain that this transaction is in the very best interests of our staff, shareholders and clients. I have spoken to a wide range of our clients, and they are all very supportive."

Martin Currie's assets under management have risen from £10.8bn at the end of 2005 to £14.4bn today. It has a global client base, with clients across Europe, North America, Africa, the Middle East and Asia.

Earlier this year the company's results for 2006 showed profits of £16.1m - up 46% year-on-year - and revenue of £80.4m - up 43% year-on-year. Sales were £3.6bn.

The new lead investor, Crestview Partners, is a New York-based firm established in 2004 by a group of former Goldman Sachs and Morgan Stanley partners who have over 20 years of relevant experience and together have led more than $20bn in acquisitions and buy-outs over their careers.

Richard DeMartini, managing director at Crestview Partners, who leads the firm's asset management strategy, said: "We make strategic, long-term investments in businesses with outstanding prospects.

"We firmly believe Martin Currie is uniquely positioned due to its ownership structure, global product focus and strong performance credentials. We are deeply impressed by Willie Watt, his senior management team and the depth and quality of the investment talent in the firm. "

Lord Rothschild said: "As clients of the firm, we have known Martin Currie for many years. Given the strength of its products and the quality of its people, we are pleased to have made this long-term, strategic investment in Martin Currie's future."

Speaking after the announcement, Watt, who spent 16 years with venture capitalist 3i, commented on the current debt crisis and its impact on the top-end mergers and acquisition landscape.

He said: "We've been here before. The market has overheated, and when that happens it forces the price of these large-scale leveraged buy-outs down. I see 2008 as being very quiet in terms of leverage action. But that will pick up towards the end of the year and into 2009, but at significantly lower prices."