A dozen sub-postmasters based in Lancashire have had their home addresses published by the Post Office on its website in a massive leak.

A document, dated from 2019, listed the names and addresses of more than 500 claimants in the ‘Alan Bates and others -v- Post Office Limited’ action in a document marked as a ‘confidential’ settlement deed.

The document is understood to have been publicly accessible as recently as Wednesday, June 19, before being removed by the Post Office.

The Lancashire Telegraph identified at least 12 claimants with Lancashire home addresses in the document, including addresses in Accrington, Blackburn, Blackpool, Preston and Lancaster.

A Post Office spokesperson said: “The document in question has been removed from our website.

“We are investigating as an urgent priority how it came to be published. We are in the process of notifying the Information Commissioner’s Office (ICO) of the incident, in line with our regulatory requirements.”

An ICO spokesperson said: “Post Office Limited have made us aware of an incident and we are assessing the information provided."

More than 700 sub-postmasters were prosecuted by the Post Office and handed criminal convictions between 1999 and 2015 as Fujitsu’s faulty system made it appear as though money was missing at their branches.

Hundreds of victims are awaiting compensation despite the Government announcing that those who have had convictions quashed are eligible for £600,000 pay-outs.

In 2017, legal action was launched against the Post Office by the 555 sub-postmasters.

Two years later, a High Court judge ruled that Horizon contained a number of “bugs, errors and defects” and there was a “material risk” that shortfalls in Post Office branch accounts were caused by the system.

The Post Office agreed to pay out £58 million to them.