Several banks and other financial institutions have been criticised for putting customers' personal information in bins outside their premises.
Customer details have been put outside the institutions' premises
The Information Commissioner's Office (ICO) has made them promise to comply with the Data Protection Act in future.
If they do not do so, they can be prosecuted by the ICO.
"It is unacceptable for banks and other organisations to carelessly discard their customers' information," ICO Deputy Commissioner David Smith says.
The institutions are HBOS, Alliance & Leicester, Royal Bank of Scotland, Scarborough Building Society, Clydesdale Bank, NatWest, United National Bank, Barclays Bank, Co-operative Bank, HFC Bank and Nationwide building society.
The Post Office and the Immigration Advisory Service were also found to have disposed of personal information in the same way.
The ICO investigation followed evidence provided by the BBC's Watchdog programme, as well as the consumer group ScamsDirect.
The Watchdog investigation found information such as details of a bank transfer for £500,000 outside a Nottingham branch of the Royal Bank of Scotland and paying-in envelopes with customer names and telephone numbers, sort codes and account numbers, at a Halifax branch in Manchester.
The ICO is an independent authority set up to promote access to official information and protect personal information.