Complaints about paid-for current accounts have more than doubled over the last year amid a sharp increase in people saying they were mis-sold one of these products, figures from the ombudsman reveal.
Some 3,107 new complaints were made to the Financial Ombudsman Service (FOS) about "packaged" accounts in the first three quarters of this financial year, surging from 1,629 cases for the whole of the year 2012/13.
The service is seeing around 100 new packaged account complaints each week, up from 40 a week this time last year - and in four-fifths (80%) of cases it is upholding consumers' complaints.
Around one in five UK adults has a packaged account, which charges them up to £300 a year for in return for a bundle of perks, such as car breakdown cover, discount vouchers and mobile phone insurance.
The FOS said the majority of packaged account complaints referred to it are about the sale of the policy.
In some cases, the customer did not even realise they had been sold a packaged account and charges for it were unclear on their statement. Some people found their account had been "upgraded" without their knowledge.
Problems also arise from paid-for perks turning out to be useless for someone's needs, such as travel insurance policies that people were too old to make a claim on. A spokesman for the service said that sometimes people had never made a claim but felt "panic" and "relief" when they realised they had been relying on a policy for which they were ineligible.
Banks have already paid out £13.3 billion to customers who were mis-sold payment protection insurance (PPI) and the ombudsman is still dealing with 6,000 complaints a week about PPI.
The ombudsman service spokesman said banks appear to be following its approach towards clearing up packaged account complaints rather than "fighting it all the way" as they had done with the PPI scandal.
A clampdown aiming to prevent unsuitable packaged accounts being pushed onto customers was introduced last spring, overseen by the Financial Conduct Authority (FCA).
To cut the risk of nasty shocks, banks and building societies now need to do more to alert customers when they are not covered by a policy on a packaged account, including sending out annual statements so people can check whether the account still suits their needs.
Richard Lloyd, executive director of consumer group Which?, said: "It's very worrying to see an increase in complaints about packaged accounts when new rules were introduced last year to protect consumers from being sold products that they don't need or can't use.
"The Financial Conduct Authority must rigorously enforce the rules to prevent mis-selling and take action against any bank that links staff bonuses to the sale of these products."
Which? previously found that one in six of its members with packaged accounts said they had only upgraded to a fee-charging account after being pressured by bank staff.
There are 58 packaged accounts on the market, charging from £6 a month to £25 a month, according to financial information website Moneyfacts. The average packaged account fee is £14 a month.
Firms buy insurance policies wholesale and offer them at discounted rates in the overall package, which can also make it hard for customers to compare costs with standalone insurance products.
Rachel Springall, spokeswoman for Moneyfacts, said: "The main issue facing the sale of packaged accounts is suitability, so until there is greater transparency of benefits on outset, complaints will continue.
"In addition, customer care and ongoing eligibility is a problem because many benefits have limitations on cover and age restrictions."
Ms Springall said that some providers, such as Barclays, allow customers to pick which "pack" they want, such as gadget insurance.
Some providers of packaged accounts have taken a step back from the market, although there have also been new entrants such as Marks & Spencer, which has been praised for tailoring its paid-for accounts to its loyal customer base.
Just over a year ago, Lloyds temporarily halted packaged account sales in branches and over the phone. It plans to re-enter the market in the coming months.
A spokeswoman for Lloyds Bank said that as a general rule in relation to sales incentives, bonuses paid to staff are now based solely on customer feedback.
Eric Leenders, executive director in charge of retail at the British Bankers' Association (BBA), described packaged accounts as "popular products that save many customers money".
He continued: "However, mis-selling of any financial product is clearly wrong. Banks have worked with the regulator to change the way these accounts are sold...
"We advise any customer who does is unsure whether they are being charged for their account should check their bank statement. If you do not think your bank account is right for you, we recommend you switch to another bank."
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