Businesses which are dismissing justified complaints from consumers about financial products are "shameful", Which? has said.

Doug Taylor, personal finance campaigns manager at the consumer group, was commenting after research published by the Financial Ombudsman Service (FOS) last week reported a significant increase in the number of complaints it upheld over the last year.

The FOS' annual report showed that the proportion of upheld complaints increased from between 30 to 40 per cent, up to 57 per cent.

Successful complaints about insurance products increased by 84 per cent, while those related to mortgages, credit cards and consumer credit rose by 34 per cent.

Mr Taylor said mis-selling, excessive rates and charges are all ongoing concerns for consumers amid the recession.

He added: "It's shameful that some firms are dismissing so many justified complaints that are upheld. This could be just the tip of the iceberg as many people give up at the first hurdle rather than going to the Ombudsman.

"Companies have a duty to treat their customers fairly and this means giving all complaints due consideration and, if appropriate, accepting them."