The insurance company, owned by Aviva, has called in the police and started legal action.

The alleged fraud, thought to have been going on over 10 years, took place within the general insurance operation which covers personal insurance and is based in Norwich.

The member of staff at the centre of the allegations works in the North West and has been suspended.

A spokeswoman at Aviva said the suspected irregularity was committed by "a number of people" in the company.

"We have issued several proceedings against a number of people following an investigation into this suspected fraud," she said.

Customers at Norwich Union, Britain's biggest insurance company, would not be affected, she said.

Norwich Union said as a result of the case it would be reviewing security measures.