NIG's commercial lines managing director Charles Earle has made a shock departure from the company.
He left the insurer on Tuesday though no explanation was given by the company as to the circumstances surrounding his decision.
But NIG announced in July this year a major restructuring of its management team.
NIG is to merge its personal and commercial lines businesses, leaving several middle managers facing an uncertain future.
An NIG spokeswoman said: "Due to confidentiality agreements signed between both parties we cannot comment on [Earle's] departure."
