BRIGHTON, England — While Aon P.L.C. says the majority of its clients have reacted favorably to its recent Berkshire Hathaway Inc.-funded sidecar deal, Lloyd's of London said it would closely monitor the structure and others like it.

In March, Aon announced a deal whereby Berkshire Hathaway would accept 7.5% of Aon retail placements in the London market where there is a Lloyd's participation.

The deal was “six months in the making,” said Stephen P. McGill, group president of Aon P.L.C. and chairman and CEO of Aon Risk Solutions. And Aon thinks it is “good for clients, good for the London market and good for Lloyd's,” he said.

“It has brought AA+ rated capacity to underpin the subscription market,” he said. By early June, more than 500 policies had been bound making use of the facility, Mr. McGill said, representing a take-up rate of more than 90%.

“I don't think there is a conflict of interest at all in the way it is being managed,” he said.

Mr. McGill's remarks were made during a CEO panel discussion during Airmic Ltd.'s annual conference in Brighton, England, last month.

“There was a lot of communication going back and forth with Aon on this,” said Vincent Vandendael, director of international markets at Lloyd's. A proliferation of such deals could have a “profound effect” on the Lloyd's market because it could risk the viability of some of the market's smaller players who, typically, help to complete line slips, he said.

“There's a proliferation risk; that's the danger here,” and Lloyd's is monitoring the situation closely, he said.

Insurers on the CEO panel said sidecars were another form of competition for traditional insurers. “I view this as Aon trying to bring a solution to clients,” said John Doyle, CEO of global commercial insurances in the property casualty division of American International Group Inc. in New York.

A broker conference atten-dee, who asked not to be named, said his company expected to pick up business as clients expressed dissatisfaction with such deals.