An investigation has been launched into allegations that a post office dumped customers' personal details in a dustbin.
Campaign group Scamsdirect claim they found post office customers' bank details, National Insurance numbers, passport numbers and other personal information in a bin on a public street.
The Information Commissioner's Office (ICO) is already investigating similar allegations against branches of the NatWest and its parent company, the Royal Bank of Scotland, in the same area and is looking into possible breaches of the Data Protection Act by the Southampton branch.
An ICO spokesman said: "The Information Commissioner's Office is currently investigating complaints concerning the disposal of personal information in Southampton.
"We have now widened this investigation. A post office in Southampton and NatWest and its parent company, Royal Bank of Scotland, are to be subject to the investigation."
He added: "Banks and other organisations that process personal information must comply with the principles of the Data Protection Act.
"Clearly, where personal information is not disposed of securely, there is a risk that it will fall into the wrong hands."
The ICO is the UK's independent authority set up to promote access to official information and to protect personal information.
A spokesman for the Post Office said it would co-operate fully with the ICO investigation.
"Security of customer information is an issue we have always taken extremely seriously and we continue to monitor and review all procedures involved in this," he said.