NIG is to open new offices in Watford and Chelmsford as part of its expanding regional commercial operation.
Its provincial commercial business has grown about 80% by business volume in the last year, the company said.
Sales and marketing manager David Grant said the new premises, added to recent expansions in Redhill and Manchester, would help the company focus on small- to medium-sized corporate clients.
NIG has also benefited from gaining £20m worth of business from agricultural network Farmweb, at the expense of Norwich Union earlier this year.
Grant said gross written premiums were forecast to hit £880m by the end of the year, up from £750m at the end of 2001.