Willis Group Holdings, the London-based global insurance broker, is to acquire a smaller rival in the US for about $2.1bn in cash and shares, kicking off what could be a wave of consolidation in the sector.

The deal to buy Hilb Rogal & Hobbs for $46 a share would expand Willis’s presence in North America. The region contributes 45 per cent to overall revenues, up from 30 per cent in 2007.