Jean Eaglesham, money policy manager at the association, said several of its members had asked for advice yesterday after it was disclosed that computer problems had caused errors on credit card accounts with National Westminster Bank, Midland, Lloyds and the Royal Bank of Scotland.
She said: 'We've been advising people to check their statements and if there is something wrong, do not pay the bill.'
If account holders paid incorrect bills it was difficult to recover the money later. The card company's ultimate sanction against the card customer was to sue for refusing to pay a bill but normally disputes were settled before this.
Ms Eaglesham said that while the problems affecting credit cards run by NatWest, Midland, Lloyds and the Royal Bank of Scotland were linked to a specific computer problem, other types of administration errors on cards were still 'worryingly common' and the association received a steady stream of complaints.
'The banks have chosen to come clean on this occasion,' she said. National Westminster continued to play down the problems, which had occurred on customers' accounts as a result of the reorganisation of the computer transaction processing system carried out between 17 and 23 July by First Data Resources, a specialist card transaction processing organisation.
National Westminster said that the main errors affecting the bank's 4.75 million Visa and Access card holders involved incorrect dates being attributed to debits on statements. But this had not resulted in incorrect calculations for interest. From today the bank will be including explanatory notes with this month's Visa and Access statements.
The main group of customers affected are holders of the bank's 250,000 Gold Cards. Midland, Lloyds and the Royal Bank of Scotland all said yesterday that only a few accounts were known to have been affected by the computer problems.