The battlelines look set to be drawn between global brokers Aon and Willis, after Aon's attempts to poach a multi-million pound team from its rival.

Willis is understood to have been so angered by Aon's efforts to take the London-based energy team it regards the move as "an act of war", market sources said.

Sources claimed that Aon has set aside millions of dollars to attract the Willis brokers. "It has a $10m war chest to target this team. It is offering to double salaries, guarantee bonuses and offer incentives. Even in competitive markets this is an aggressive move.

"It seems there's an element of 'let's get them' - both the team and Willis in general."

Aon's move comes only months after the Willis energy team had been reinforced with a number of new recruits. Willis itself took six brokers from Marsh, one from Millers and two were to join from Aon in the autumn.

The Marsh brokers were: Paul Braddock, Chris Colman, Chris George, Alan Nash and Neil Smith. Steve Portman joined from Millers, while Gerard Maginn and Jeremy Bennett were joining from Aon.

Rates in the energy sector have rocketed since last year's devastating Atlantic hurricane season, with increases of as much as 50% being reported.

Willis has also lost a number of brokers from its Latin America and Southern European team based in London. It is believed Willis chief executive Joe Plumeri flew over to London in an attempt to persuade them to stay.

The Willis unit head, Alberto Carrara, is understood to have resigned to go to Aon, and has been followed by other team members. These include D&O and financial institutions specialists Luca Tassarotti, Andrea Guffanti and Enrico Nani. Sources said they were also expected to emerge at Aon's London-based professional risks division.

Jeremy Wall is understood to have resigned but is now staying at Willis.

An Aon spokesman said: "We will not be commenting on speculation around possible recruits other than to say that attracting and retaining unmatched talent to the organisation is one of Aon's key goals."

Willis declined to comment.