The survey, which singles out NatWest for the most criticism, found that one in seven of those surveyed had money incorrectly taken from an account and one in eight had been charged incorrectly - an increase from last year, when the proportion was one in 10.
The results follow the publication last week of the Banking Ombudsman's annual report, which showed a continuing high level of complaints.
According to Which?, the code of banking practice introduced in March 1992 promised a new era of improved standards of service which 'never happened'.
Which? describes the code as a 'dismal failure'. Dr John Beishon, chief executive of the Consumers' Association, said: 'With a minority of praiseworthy exceptions, the high-street banks and building societies continue to mishandle customers' accounts to an astonishing degree. They are guilty of ineptitude compounded by complacency, and it goes on and on. Nothing has improved since last year.'
He added: 'Last year, little had changed since the year before.'
Among the examples quoted are a woman who was charged pounds 32.50 by the Bank of Scotland for exceeding an overdraft limit she had not been told about and a man who had pounds 850 withdrawn from his NatWest account because of a 'mix-up'.
More than 3,600 took part in the survey, which found that one in 10 were dissatisfied with the management of their current accounts, one in five with information on charges and one in four with information on interest rates.
Insitutions which registered the highest levels of satisfaction were the Abbey National, First Direct, Girobank and Yorkshire Bank.
Those wanting charity Christmas cards are advised by Which? to buy them from charity catalogues or charity shops, rather than high- street retailers, since more of the price goes to the charity.
In ordinary shops, as little as 5p for every pound spent on cards may go to the charity. For example, five cards sold in John Lewis Partnership outlets cost pounds 1.95, of which 10p is given to Shelter.
The same card is sold in packs of 10, costing pounds 2.95, in Shelter's catalogue. Buying direct from Shelter saves the customer nearly pounds 1 and increases the charitable donation to pounds 1.40.
Subscribers report on debit side of operating an account
Three 'Which?' subscribers give accounts of their troubles with banks.
ROSEMARY SEY, a Bank of Scotland customer, was sent an out-of-date list of charges and incorrect details on her additional overdraft. Although she repaid the extra overdraft, the limit on her current one was reduced without her knowledge. As a result she exceeded her overdraft limit and was charged pounds 32.50. She had to write three times before the matter was corrected.
LLOYDS BANK paid a direct debit order on Anthony Titmarsh's account, even though he had never authorised the payment. He complained, but did not receive an adequate explanation. His claim of pounds 105 compensation was refused: Lloyds, who could not produce a direct debit form for the payment, offered pounds 50 and refused to accept any blame.
GIROBANK wrongly cancelled direct debit orders made by John Skinner, a Middlesex social worker, to pay his poll tax and a magazine subscription. The bank admitted responsibility, and offered pounds 35 compensation to Mr Skinner. The Banking Ombudsman ultimately awarded him pounds 150.Reuse content