NOW there's another Willis building - and it's the biggest one yet.

NOW there's another Willis building - and it's the biggest one yet.

The global insurance broker, known in East Anglia for its iconic black glass-clad offices in Ipswich, last year transferred its entire London operation into a brand new building at 51 Lime Street, one of the largest office blocks in the City at a height of nearly 125 metres.

And now the New York-listed company has gone one better - or 317 metres better to be more precise - by applying its name to the tallest building in the western hemisphere.

The former Sears Tower in Chicago, which opened in 1973, was yesterday officially renamed the Willis Tower in a ceremony involving Willis Group chairman and chief executive Joseph J Plumeri and the Mayor of Chicago, Richard M Daley.

The renaming comes as a result of Willis taking more than 140,000 sq ft of space within the building which will see nearly 500 employees relocating from five smaller offices.

The 442-metre tall tower - the tallest building in the world when completed - was originally built for the US retailer Sears which sold the building in 1994 and moved out the following year.

It is now owned by an investment group formed to purchase the tower in 2004 and the naming rights acquired by Willis as part of its tenancy deal will last for 15 years.

“Every member of the Willis family is honored to be associated with such an architectural icon and privileged to call this prestigious business address our new Midwest Region headquarters,” said Mr Plumeri.

“Willis has been in Chicago since 1885, the same year that William LeBaron Jenney built the Home Insurance Building, the first skyscraper in the world. Over the years, we've grown as Chicago has grown, and we are delighted to be a part of the great future this dynamic city is building as a global financial centre.”

At yesterday's ceremony, Willis presented a check for US$100,000 to the Chicago Cares voluntary organisation, and the company is donating a similar sum to the Chicago 2016 campaign to bring the Olympic Games to the city.