The UK's Information Commissioner's Office - which enforces the Data Protection Act - said in August that it was investigating claims that high street bank NatWest, which is owned by the Royal Bank of Scotland, allegedly dumped customers data in an outside rubbish bin.

The investigation was triggered by a complaint from consumer group Scamsdirect which accused NatWest of failing to dispose of customer information securely after it found customer details dumped outside a RBS/NatWest branch in Fareham, Hampshire.

According to a report by the Times newspaper the Information Commissioner Richard Thomas has now widened the investigation to include HSBC and the Post Office.

He told the newspaper that he had received "highly disturbing evidence" that customer data, including bank statements and loan applications, had been dumped in bin bags on the street outside branches.

"There have been cases now which have quite strong prima facie evidence which we are urgently investigating, of banks’ rubbish bags found on the public highway outside banks," Thomas told The Times. "I have seen some of these where, open up the rubbish bag and there you find bank statements."

According to the report, cases being examined by the office include an application for a current account - including all the customers' details - which was found in the rubbish, as well as a loan application form that included personal details. Photocopies of bank statements with account numbers and a mortgage application letter have also been found in rubbish bins.

Thomas says members of the public and bank employees have also complained about the lax security.

He says the office is considering taking enforcement action against banks that dump data, which may result in "unlimited fines".

ID theft is estimated to cost the UK economy £1.7 billion and affects more than 100,000 people every year, according to figures from the UK's National Consumer Council (NCC).