A Christchurch lawyer is urging disgruntled customers of a major earthquake claims-holder to join "no win, no fee"class action lawsuit.

GCA Lawyers, headed by Grant Cameron, took on the case last year against Southern Response, claiming the insurer had imposed unjustifiable delays in processing and settling earthquake claims.

Homeowners were reluctant to pay about $2000 in fees and face the risk of having to pay for an expert and adverse costs in case the action was unsuccessful.

The law firm had now found an international backer for the potential $1billion class action case, Cameron said Tuesday.

This meant homeowners would not have to pay for anything to join the action and were not at risk to face adverse costs.

If the action was successful, the firm backing the claim and GCA would take up to 20 per cent of the amount awarded in damages.

The backer, international consortium Litigation Lending Services, would pay any upfront costs, including engineers and other experts, and would take on the risk of paying for adverse costs if the case was lost, he said.

Cameron said the backer only funded actions where its lawyers considered there was a "high likelihood of success".

"Our litigation funder can get independent experts to tell you the real value of Cantabrians' claims, and fight for damages including anxiety, stress, relocation, rent, storage and any other cost because of payout delay," he said.

Each claimant could get anything from $10,000 to $30,000 a household for costs and an additional $25,000 to $50,000 for intangible costs such as stress.

"Southern Response is only meeting 40 to 50 per cent of the amounts claimed based on its own inadequate building reports," Cameron said.

He needed 200 claimants for the action to go ahead.

Cameron believed there was potential for more than 3000 claimants to come forward.

At the end of March 2015, Southern Response had settled 4280 over cap claims. It had yet to settle 2256 claims.

Southern Response did not respond to requests for comment on the class action on Tuesday.