The former subpostmaster and campaigner Sir Alan Bates is calling on the government to set a deadline of next March to pay redress to the hundreds of victims who helped to uncover the Horizon IT scandal.

In a message addressed to other subpostmasters involved in the Group Litigation Order (GLO), Sir Alan raises concerns that some older participants are settling claims sooner “just to get it all over with”.

He questions whether the government is dragging the “issue out to exhaust victims until their deaths” and if the scheme has become a “gravy train” for its lawyers.

A government spokesperson said ministers would continue to meet with those affected “to get swift and fair redress paid”.

Between 1999 and 2015, more than 900 subpostmasters were wrongly prosecuted after faulty software called Horizon indicated that money was missing from Post Office branch accounts.

Sir Alan leads the Justice for Subpostmasters Alliance, campaigning for financial redress for the 555 victims who took part in the landmark group legal action against the Post Office.

Their compensation was, however, swallowed up by the huge legal costs involved in bringing their case.

The government went on to set up a specific compensation fund to give these subpostmasters the same as others affected, but progress has been described as slow.

Of the hundreds of members of the GLO group, 63 had criminal convictions and therefore are not eligible for this scheme but they are eligible for other compensation – depending on how their convictions are being overturned.

According to the latest government figures, 201 of the eligible 492 subpostmasters in the GLO scheme have received their payments in full.

More than 250 offers have been made through the scheme, while people can challenge them and decisions may be reviewed by an independent panel.

But in his latest newsletter to the GLO group, Sir Alan said the Department for Business seemed to be trying to get away with paying out as little as possible to victims while maximising the income for the legal firms involved.

He also suggests it employs “flim-flam artists” who were dragging the process out and burying the scheme in bureaucracy, while dismissing suggestions on how to speed matters up.

He estimates that some £500m has been spent so far on legal fees associated with the scandal, and describes it as something the Public Accounts Committee “should be investigating as a matter of urgency”.

To drive things forward, Sir Alan says it is time for a guaranteed commitment for all claims to be paid out by March 2025 – three years after this particular compensation scheme was announced.

“We need to get the message out that a March 2025 deadline has to be set,” he wrote.

Imposing a deadline for payments has been ruled out in the past, for fear that some subpostmasters might be timed out of claiming compensation.

Sir Alan also said that he would be prepared to go back to court if “excuses” were made and that he would be meeting with new law firms to discuss the matter in the coming weeks.

A spokesperson for the Department for Business and Trade said: “It isn’t acceptable that subpostmasters feel they aren’t being listened to or have their claims drawn out.

“Our ministers will continue to meet with those affected and work with them to get swift and fair redress paid.”

They said that since July the government has taken “swift action” in launching the new Horizon Convictions Redress Scheme and announcing a new appeals process in the Horizon Shortfall Scheme in order to speed up payments further.

They added that the department is making 90% of initial offers within 40 days of receiving completed claims, and encourages other subpostmasters to come forward “as soon as possible to claim back what they are owed”.

The Horizon IT scandal captured the wider public’s imagination after the ITV drama Mr Bates vs The Post Office was broadcast earlier this year.

It garnered a huge response and saw a new law quashing the wrongful convictions of hundreds of subpostmasters introduced in May.

Last Thursday, however, former subpostmistress Jo Hamilton also criticised the government for a lack of action on the scandal as she collected a National Television Award surrounded by fellow victims, saying: “I went to Westminster a couple of weeks back and saw the new minister and trust me, nothing has changed.”

In response to her comments, ministers said they were working “tirelessly” on the compensation schemes for those affected.

The prime minister also said the government would compensate the victims of the Post Office scandal “just as quickly as we can”.

Asked about Ms Hamilton’s remarks, Sir Keir Starmer said he would “stick by” his commitment to pay the victims’ compensation.