The former subpostmaster Lee Castleton, one of the highest-profile victims of the Horizon IT scandal, has become the first individual to launch legal action against the Post Office and Fujitsu.

Castleton, who was played by the actor Will Mellor in the hit ITV drama Alan Bates vs The Post Office, was made bankrupt by the Post Office after a two-year legal battle.

His case is one of the most well-known in the Horizon IT scandal, which has been described as the most widespread miscarriage of justice in UK history.

Castleton bought a post office in Bridlington, East Yorkshire, in 2003. However, within a year his computer system showed a £25,000 shortfall despite him calling the Post Office’s helpline 91 times, as he suspected the flawed Horizon IT system, supplied by Fujitsu, was at fault.

He was taken to court by the Post Office, where he had to represent himself as he could not afford a lawyer, and was ordered to repay the money and pay costs of £321,000, which bankrupted him.

Castleton is seeking compensation, alleging the civil judgment against him was obtained by fraud.

“I want justice and to be publicly vindicated,” said Castleton, who is due to receive an OBE next month. “I’d like to effectively have my day in court as well.”

While other victims have seen their convictions overturned, Castleton’s civil judgment against him still stands. His legal action is to set aside, or overturn, the judgment.

In 2023, the public inquiry into the Horizon scandal heard that the Post Office knew that Castleton would probably be bankrupted if a legal case was brought against him, but it wanted to send a warning message to others.

Stephen Dilley, who represented the Post Office in the civil claim against Castleton, told the inquiry into the IT scandal that it knew he would not be able to pay if he lost but that the state-owned company wanted to “show the world” it would defend the Horizon system.

After the legal action, Castleton was forced to close his shop, sell his house and move into rented accommodation, while his wife suffered stress-induced seizures and his children had to move schools because of bullying.

Castleton has instructed his solicitors, Simons Muirhead Burton, to issue proceedings at the high court against the Post Office and Fujitsu on his behalf.

In November, Alan Bates, the lead campaigner for justice for post office operators, suggested that operators could take fresh legal action if “full and fair” claims through the government’s compensation scheme were not finalised within a reasonable timescale.

“If deadlines are not set for the schemes to be finished then there’s every chance … it might be quicker for us to go back to court,” he told the business and trade select committee of MPs.

Castleton has never applied to the government compensation scheme, but automatically received an interim payment.

In her debut budget last October the chancellor, Rachel Reeves, said that the government had set aside £1.8bn to cover all compensation claims.

There are four main schemes – Horizon Shortfall, Group Litigation Order, Overturned Convictions and Horizon Convictions Redress – which, as the sole shareholder of the Post Office, the government is responsible for paying out.

As of the end of January, the government said that approximately £663m had been paid to more than 4,300 claimants across the scheme, including interim payments for people whose full case had not been settled.

Compensation payments that have been made so far range from £10,000 to well over £1m.

The Post Office and Fujitsu have been approached for comment.