ABOUT 240 partners in Watson Wyatt LLP, the UK actuaries, are to share $451 million (£240 million) in cash and shares after selling out to Watson Wyatt & Co, their American alliance partner.

The Wall Street-listed sister company is buying the 80 per cent of Watson Wyatt LLP that it does not already own. The average payout of £1 million per partner spells the end of independence for the UK firm, which was founded as R Watson in 1878.

The move represents the biggest deal in the actuarial profession since 2002, when Hewitt Associates of the US took over Bacon & Woodrow to form Hewitt Bacon & Woodrow.

The 45 main equity partners in Watson Wyatt LLP will receive the lion’s share of the payment, which comes in the form of $158 million in cash and the rest in the US company’s shares.

They include senior partner Paul Thornton, a Watson veteran of 30 years, and managing partner Babloo Ramamurthy, who will both join the combined organisation’s board.

Junior partners will receive a lesser share and the remaining 1,760 employees of the business, based in Reigate, Surrey, will get nothing.

The US alliance goes back to 1995. “It’s been a long honeymoon, a Watson spokesman said. “We want to be more joined up so we can serve our global clients better.”

Watson Wyatt LLP claims relationships with 75 companies in the FTSE 100, advising either them or their pension funds, or providing other personnel advice.

Clients include British Telecom, British Airways and ICI. In revenue terms, only Mercer’s is bigger than Watson.

Rival firms said that the UK partners may have decided the time was right to sell out because of imminent reforms in the profession that are aimed at reducing potential conflicts of interest. The firm is renowned for advising both pension funds and their sponsoring companies and could lose some clients as a result.

Mr Thornton said the full merger would streamline governance and decision-making. The combined organisation will employ 6,000 people in 30 countries and bring in estimated annual revenues of $1.1 billion.

The Wall Street listing would also give the firm access to capital to make acquisitions and to upgrade IT.

A $50 million portion of the purchase price is dependent upon the British-based side of the business achieving performance targets up to June 2007.