NIG is believed to be facing a multi million pound claim as insurer for Big K, the barbecue fuel manufacturer, which went up in smoke last Saturday.
Some 90 fire fighters battled the blaze, which happened at the company's production plant at Stoke Ferry, Norfolk.
The fire, which raged across an area the size of a football pitch, burned for several days.
Crawford is the loss adjuster, while Balcombe Group is acting as loss assessor for Big K.
No one was injured in the fire, but the nearby A134 road was closed because of smoke. The cause of the fire is being investigated.
NIG confirmed it was the insurer but a spokeswoman said there was no information available.
Crawford stated it was unable to give details on its involvement.