Cunningham Lindsey has been appointed as the sole loss adjuster for the Co-operative Insurance Society (CIS).
The appointment follows the insurer's decision to abandon the use of a panel of loss adjusters.
CIS would not say which loss adjusting firms were previously used by the company, although GAB Robins is thought to be one.
Terry Witter, head of central sourcing and field operations at CIS, said: "Over the last few months CIS has been giving careful consideration to its needs for loss adjusting services, looking ahead to the next few years."
CIS announced a two-year modernisation programme in 2004.
The insurer said the detailed review was a direct response to market and economic changes.
The review was designed to ensure future profitability and growth, according to CIS.
Mark George, client relationship director at Cunningham Lindsey UK, said: "We are delighted to have secured our relationship with the CIS.
"We have worked with it for a very long time and it is a key client for us."
Cunningham Lindsey was appointed to the loss adjusting panels of both Fortis and RBS Insurance in January of this year.