In a complicated transaction, KKR, which has some $91bn (#55bn) invested on behalf of long-term investors such as US state pension funds, will acquire 76% of Trinity Acquisition, the vehicle set up to carry out the purchase. Five insurance companies are putting up #193m for a 19% stake in Trinity, while the remainder of the equity will be held by Willis management led by chief executive John Reeve.

KKR's Perry Golkin said he would be investing for the long term and would be prepared to put substantial additional funds into Willis to help expansion. KKR's biggest investment so far in Britain has been backing the #205m buy-out of Reed Regional Newspapers in 1995 to form Newsquest.

The deal seems to be sewn up as fund manager PDFM has sold 9.9% of Willis to KKR for 201.75p, including a 1.75p interim dividend, and has accepted irrevocably for another 9.2%.