Towergate Partnership is aiming to snatch £100m of SME premium income from rival brokers.
The assault will be driven by a call centre operation combined with internet sales.
It aims to win £100m of premium within two years: equivalent to the SME book of Allianz Cornhill.
The broker giant said it was responding to threats from both insurance companies and imarket by buying an existing operation that would allow it to rapidly expand its SME offering.
Towergate Partnership chief executive Andy Homer said: "Rather than wait for a technical solution to be provided by the manufacturers we believe brokers should not hang about.
"This is a natural market for brokers who have access to a much wider range of products than insurers do."
Homer added that while he considered imarket to be both an opportunity and a threat, there was a possibility the portal would lead to "disintermediation".
He said: "We only want to pass information across the imarket network, which is the minimum required."
Though Homer refused to be drawn on the identity of the acquisition he confirmed that the group was looking to make at least five further acquisitions over the next few weeks.
He said: "We are currently writing about £1.1bn gross written premium which should rise to £1.5bn by the end of the year."
However, he warned that prices were falling from around 1.4 times brokerage to around one times brokerage as the market softened.
Three banks poised to refinance Towergate
Towergate Partnership chairman Peter Cullum said the company had received a number of approaches about financing its estimated £350m debt.
Investment banks including HBoS, Barclays and Lloyds TSB are now in the frame to usurp Royal Bank of Scotland as the group's primary backer.
He said: "If all things were equal it would be great to stay with
Royal Bank of Scotland, but it is a cutthroat world."