Insurance companies are increasingly refusing to pay out money to policyholders for motor, household and health claims, brokers have claimed.

The British Insurance Brokers' Association (Biba) said 90% of members it questioned believed insurers had become more strict on paying claims, largely because of the economic climate and fraud.

Almost two-thirds of brokers said they have had to fight harder to get claims paid, and nearly three-quarters have successfully appealed against a claim rejection by an insurer in the past year.

The assertion is backed up by findings from the Financial Ombudsman Service (FOS), which deals with claim disputes which cannot be resolved by the insurer and its customer.

In the past year the ombudsman has seen a 12% increase in complaints about insurers, the majority of which are about disagreements over claims.

"We are finding that insurance disputes are being harder fought on both sides," a spokesman for the FOS said. "One way insurance companies are controlling costs is by fighting insurance claims harder."

In the financial year to March 2012, the FOS saw a 26% increase in complaints relating to motor insurance from the previous year, a 31% increase in buildings insurance complaints, a 23% rise in disputes about contents insurance, and a 55% increase in complaints involving critical illness insurance.

In its report the ombudsman said: "It is disappointing when insurers continue to pursue cases to the final stage – requesting final decisions from an ombudsman – in areas where our approach is well known and clearly set out."

In the case of motor claims it said: "Insurers can still be too quick to assume thefts are not genuine.

"We have also had concerns in some cases about the way in which the insurer has investigated issues around 'non-disclosure' by the consumer. This has included disputes where the insurer had not properly considered whether the questions they asked the customer – or the questions on a comparison site – were sufficiently clear."

Biba cited the case of an insurer that wrongly rejected the claim of an armed forces family posted overseas. While abroad the family put their belongings into storage; when they returned the belongings had been damaged, so they took steps to claim from the insurance policy of the storage company.

"The claim was unsuccessful due to policy wording interpretation from the insurers, and the family was offered £4,000 – although their belongings were worth significantly more," a Biba spokesman said. "An insurance broker became involved and helped the family navigate the policy wording and evidence that their claim was valid, resulting in it being settled for £12,000."

The Association of British Insurers said it rejected Biba's research claims. Nick Starling, director of general insurance, said: "We do not accept any suggestion that it is getting more difficult for genuine claimants to be paid and we have seen no evidence pointing to this.

"The priority of insurers is to pay all genuine claims as quickly and efficiently as possible."

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