A number of sub postmasters across North and West Cumbria have been affected by a massive data leak by the Post Office.

The data breach involved a document which 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.

Three sub postmasters from across North and West Cumbria were identified as part of the data breach and a further sub postmaster was also identified in the south of the county.

The Post Office has come under fire since the airing of the ITV drama Mr Bates Vs The Post Office, which put the Horizon IT scandal under the spotlight.

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

Mr Bates had his contract terminated by the Post Office in 2003 after refusing to accept liability for shortfalls in the accounts at his Llandudno branch in North Wales.

The scandal has been called one of the largest miscarriages of justice in British history and has provoked anger from across the political spectrum.

Hundreds of sub postmasters are still awaiting compensation despite the Government announcing that those who have had convictions quashed are eligible for £600,000 payouts.

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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."