Britons are increasingly ready to complain in restaurants and shops, but we remain reluctant to take action when we feel our current account provider has let us down.

According to Nationwide, despite our reputation for reticence, we are more likely than anyone else in Europe to speak up about poor catering or retail service. Yet, when it comes to dissatisfaction with banks, the only people less likely to make a fuss are the Germans.

Fewer than a fifth of respondents to the building society's survey said they were likely to change their account provider in the near future, with a third saying it wasn't worth switching because all banks were basically the same.

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Danielle Pafford, a co-founder of independent switching service, said: "Quite a large number of people are unhappy with their bank. It ranges from those who are really frustrated with the service they're getting to those who are frustrated with the banking system in general.

"But there's a huge amount of inertia, which partly reflects the structure of our banking system: five big banks have a 90% market share.

"More people would move if they knew more about the alternatives and that there are local, mutual and ethical options."

Under the switching service, introduced last September, account providers must ensure all switches are completed within seven working days of the new account being approved. All regular payments to and from the old account are automatically moved to the new one, with a redirection continuing for 13 months, so annual payments such as subscriptions are not missed, and any fees or charges incurred because of errors during the process must be refunded by the new provider.

Between October and December, 306,240 people moved their account, a 17% rise on the last quarter of 2012, and the trend is gathering momentum, with 83,729 of those switches taking place in December, a 54% increase on the year before. These include smaller high street banks and internet-based account providers, mutually owned building societies and credit unions.

This week the two biggest challengers launched new charm offensives to win new customers. The Cooperative Bank will pay new customers £125, of which £25 of will go to charity.

Andrew Hagger at said: "It's been a very troubled few months for Co-op Bank but it's good to see it back and fighting for new current account customers.

"Despite the high profile issues with the behaviour of former directors and fall-out regarding the £1.5bn rescue package, at a branch level it's been business as usual with the excellent customer service for which it has been renowned over the years, still much in evidence."

Nationwide meanwhile has launched 'Refer a Friend', where an existing customer recommends a new one and the £100 reward is split between both parties.

Up to 10 referrals a year (worth £500) are allowed.

Mr Hagger said: "With some of the better current accounts on the market, I'm sure existing customers will have few qualms in recommending the UK's biggest mutual to friends and family fed up with poor deals and/or sub-standard service. Both of these incentives are worth a closer look, but it's more about finding an account that mirrors the way you run your finances than short-term incentives."

But new research from Which? shows most people cannot understand the costs of a current account. The consumers' organisation asked a group of volunteers to work out the total interest and fees levied for accidentally going over the agreed spending limit on the 12 biggest providers' main current accounts.

The volunteers, who were provided with mock statements and the banks' web addresses, got just 10 out of 72 unauthorised overdraft calculations right between them. Even a principal inspector of taxes got only one out of four, and a retired headteacher was wrong every time.

Which? says overdraft charges are becoming harder to access and understand, with an array of baffling terminology, conditions and calculation structures.

It took the volunteers an average of 10 minutes to find the information they needed online, compared to four minutes during similar research two years ago, and they got fewer calculations right than before.

Which? executive director Richard Lloyd said: "Consumers are faced with myriad complicated charges for using an unauthorised overdraft, and it's virtually impossible for people to calculate and compare the cost of running a current account."

But according to Which? a poor choice of account could leave you out of pocket by more than £2000 a year.

It said Nationwide FlexDirect was the best account for someone who was always in credit, while they would be worst off with Bank of Scotland, Lloyds or TSB Classic.

For those requiring a small authorised overdraft, Clydesdale and Yorkshire Banks' Current Account Direct was the most cost-effective choice, while Bank of Scotland, Lloyds and TSB Classic were costliest.

For a large authorised overdraft, Clydesdale and Yorkshire were best again, with Santander Everyday the most expensive.

For large and small unauthorised overdrafts, Halifax Reward were cheapest, while Clydesdale and Yorkshire charged most for small amounts,. Bank of Ireland charged most for large sums.