Another three quarters, meanwhile, feel that nothing about their banks has changed since last year.
And almost 9 million (18%) customers would not recommend their current bank to family and friends. Of these, four in 10 are dissatisfied due to the poor customer service they receive, while 30% feel that their banks do not treat them as individuals.
Huw Davies at Triodos Bank said: "Surely it should be possible for banks to do more and make things better for their customers and for society as a whole."
The relationship Britons have with their banks is not the only reason they are unhappy, though. Almost a quarter of those who would not recommend their current bank to a friend or relative said the main reason was the bonus culture that ensured the bank's high-flying employees received large salaries, even when the economy - and the banking sector - was in trouble.
That is not the only gripe consumers have, though. A massive 24% of respondents also said that their dissatisfaction was at least partially due to their bank failing to offer sufficient finance to cash-strapped UK businesses and consumers.
Triodos Bank is therefore urging Britons unhappy with their banks to take matters into their own hands and move their accounts elsewhere. "With so many Brits feeling fed up and dissatisfied with banks at the moment, we'd like to challenge people to vote with their feet, and move to a better bank," Davies said.
He could have a difficult job on his hands, though. Figures show that we are more likely to get divorced than to switch our current accounts.
And Triodos' own research supports this, with some 13% of the people who responded to its survey stating that they are still with the bank their parents set them up with as a child.
While the reasons for people's dissatisfaction range from poor service to how a bank allocates its funds, the study also found that only 7% chose their bank because it offered the best interest rates.
That, however, is a great shame when you consider that the market-leading current account - Santander's Premier Direct - is paying 5% on up to £2,500 for the first 12 months, while many of the big bank's most popular accounts pay nothing at all.
For those in the red, the account also offers a year-long, interest-free overdraft, which could help you to avoid authorised borrowing charges of 18% or more with many other banks, and is even giving new customers a switching incentive of at least £100.
With so many households feeling the pinch, surely that should be enough to convince them to make the switch?