LONDON—Willis Group Holdings P.L.C. said Tuesday that its revenue increased 4% in 2011, driven in part by improved business retention and an uptick in new clients.

The London-based brokerage also said it would begin accepting contingent commissions on employee benefits business, effective April 1.

For 2011, Willis reported total revenue of $3.45 billion, up from $3.33 billion in 2010. Willis attributed much of the increase to 2% in organic growth of its commissions and fees, which benefited from net new business and higher retention rates.

Net income dropped to $219 million last year, down nearly 52% compared with 2010. The decrease included a $180 million pretax charge related to Willis' 2011 operational review, which included staffing cuts and facility consolidations. The cuts generated $80 million in cost savings last year for Willis, the company said in a statement.

Willis' North America segment reported $1.32 billion in commissions and fees for 2011, a 4% decline from 2010. The brokerage said the decrease resulted in part from the loss of accounts and "poor performance" in Willis' U.S. loan protector business, a lender-placed insurance segment that Willis acquired in 2008.

However, the company's overall performance was boosted by its international segment, where Willis saw organic commissions and fees growth of 2% and total commissions and fees of $1.03 billion, and its global segment, which saw organic commissions and fees growth of 6% and a total of $1.07 billion. The global segment comprises reinsurance, global specialties and other business.

“While the fourth quarter and, indeed, the full year of 2011 included many achievements for which Willis can be proud, our measure of organic growth demonstrates the challenges that our business endured in the final months of the year and shows where we must improve in 2012,” Willis Chairman and CEO Joe Plumeri said in the statement.

For the fourth quarter, Willis reported revenues of $825 million vs. $833 million in the year-earlier period. Fourth-quarter 2011 net income was $40 million, down 59% compared with a year ago.

Willis also said it would begin accepting contingent commissions on its employee benefit business as of April 1. During an investor call Wednesday, Mr. Plumeri said the brokerage was forced to do so because of changes in the way employee benefit insurers compensate brokers as a result of health care reform.

He stressed, though, that the change affects only employee benefits business.

“We have long taken a strong stance against accepting contingent fees in any of our retail business,” Mr. Plumeri said. “We will continue to take the position across the remainder of our product line.”

He said, however, that a result of the change in its employee benefits business, Willis is also reviewing its corporate policies, public documents and its compensation disclosure processes generally.

He said Willis will work closely with clients and insurers to implement the changes, and will continue to “always act with integrity and in its clients' best interests.”

During a question-and-answer portion of the investor call, Mr. Plumeri said Willis probably would earn $4 million to $5 million from employee benefit contingent commissions this year.

Willis stopped accepting contingent commissions amid then-New York Attorney General Eliot Spitzer's probe of the insurance industry. Willis has accepted some commissions on business it gained with its 2008 acquisition of Hilb Rogal & Hobbs Co., although it has been phasing out such pay.

Meanwhile, a company spokeswoman confirmed that Willis had taken down its “clients before commissions” Web page, although she could not immediately provide further detail.

Mr. Plumeri also fielded a question about his future in the face of a report that he would step down next year. He said his contract expires July 7, 2013. “The board is in the business of continually discussing succession,” Mr. Plumeri said. “They have been doing that. They will continue to do that. That's what boards do.

“What Joe Plumeri does is run a company. I spend my time doing that and I intend to do that, certainly until my contract is over and that's what I'll concentrate on doing,” Mr. Plumeri said.

Mark A. Hofmann contributed to this story.