Willis Group has put 20 million of its shares on the New York Stock Exchange. Underwriters will also have the chance to buy an additional three million, if demand for those shares is too great.

The world's third largest insurance broker announced its intention to make an initial public offering of shares in April. It filed a registration statement with the Securities and Exchange Commission last week (May 16).

Willis's parent company intends to use the proceeds from the sale to redeem preference shares of one its subsidiaries, TA II, or to repurchase senior subordinated notes from Willis North America (or both).

Kohlberg Kravis Roberts (KKR), the US firm that purchased Willis in 1998 for £851m, confirmed it had no intention of selling its shares.

Chairman and chief executive officer Joseph Plumeri, who joined Willis last year after 32 years at Citigroup, has repeatedly denied that he is working on behalf of KKR to sell on the company. But in the past, he has admitted that going public is something to “aspire” to.

Willis currently employs more than 12,500 employees and has 235 offices in 73 countries.