When the Post Office/Horizon ITV drama starring Toby Jones aired in January, there was a huge public backlash.

Jones starred as Alan Bates, who along with his partner Suzanne Sercombe used all his savings to buy a Post Office branch in Llandudno, North Wales.

Their life - and that of many others - is turned upside down when the new computer system called Horizon is installed in branches across the country.

As a result of errors in the technology, numerous postmasters were wrongly prosecuted between 1999 and 2015 after being accused of fraud, theft and false accounting.

Since Mr Bates Vs The Post Office was broadcast 50 new potential victims have approached lawyers.

The Post Office is wholly owned by the Government and a public inquiry into Horizon is ongoing.

Speaking during a visit to Oxford on Sunday, the Prime Minister said the UK Government was “keen to do everything we can because this was appalling” and should “never have happened”.

What is the Post Office Horizon IT scandal all about?

Between 1999 and 2015 the Post Office relentlessly pursued operators of sub-post offices across the UK for alleged theft, fraud and false accounting based on information from its Horizon IT system installed in the late 1990s.

That was despite knowing that from at least 2010 onwards there were faults in the centralised accounting software.

In total, about 3,500 branch owner-operators were wrongly accused of taking money from their businesses, with more than 700 prosecuted by the Post Office despite protesting their innocence and raising issues with the software in their defence.

The scandal is frequently described as the most widespread miscarriage of justice in UK history.

What harm did it cause?

Hundreds of sub-post office operators ended up with criminal records and punishments ranging from having to do community service and wear electronic tags to being jailed. Many were left struggling financially or even bankrupt following convictions. Even those who did not go to court had to drum up money to cover nonexistent shortfalls.

Victims and their families were severely hit by stress and in many cases illness, with the scandal linked to at least four suicides.

For years the Post Office, which has the power to investigate and prosecute without the need for police involvement, continued to defend itself against accusations and press reports highlighting problems with the IT system, developed by Japan’s Fujitsu, including through legal means.

In 2019, a group of post office operators won a high court case in which their convictions were ruled wrongful and the Horizon IT system was ruled to be at fault. In 2021, the ruling was upheld on appeal, quashing the convictions of some workers who were wrongly accused of committing crimes, paving the way for compensation.

However, even since the computer system was found to be defective, the Post Office has still opposed several appeals by operators.

What about those who pursued the prosecutions?

To date, no Post Office staff have been punished for the scandal. On Friday, the Metropolitan police confirmed for the first time that the Post Office is under criminal investigation over “potential fraud offences” committed during the scandal.

The Met is already investigating two former Fujitsu experts, who were witnesses in the trials, for perjury and perverting the course of justice.