The deal is worth £100 million and was backed by mid-market specialist Graphite Capital, which invested £50 million in the transaction in return for a ‘substantial majority stake’ in the business.

Further finance was provided by HSBC, including acquisition finance, senior debt and invoice discounting facilities. All members of the management team are also said to have made significant investments.

The buy-out was led by chief executive Rosaleen Blair, who founded AMS in 1996 as a venture subsidiary of recruitment group Alexander Mann. The company was acquired by Advent Capital in 1999 and now constitutes the entire group, with turnover of £340 million in the year to September 2007.

Mike Tilbury, partner at Graphite Capital, comments: ‘[AMS] has won long-term contracts with some of the biggest companies in the world and has a clear strategy for growth with existing and new clients in Europe, the Far East, Australasia and North America.’

AMS operates by embedding its staff in client companies, which typically sign up for multi-year contracts. It operates in 50 countries and has 900 employees.

Graphite Capital manages £1.2 billion through three private funds and the publicly quoted Graphite Enterprise Trust. The firm raised £475 million in May for its latest fund, Graphite Capital Partners VII, which backed its investment in AMS.