The Japanese tech company at the centre of the Post Office IT scandal is facing calls from a parliamentary committee to make an “immediate” payment towards the compensation bill for victims.

Fujitsu supplied the faulty Horizon software to the UK Post Office, which led to branch operators being wrongly prosecuted over discrepancies in their business accounts.

The scandal has been described as the worst miscarriage of justice in British history and was the subject of the acclaimed ITV drama Mr Bates vs the Post Office. Thousands of post office operators are waiting for redress.

Liam Byrne, the Labour MP who chairs the business and trade committee, said “justice delayed has become justice denied” for too many victims, and urged the government to “do whatever” it took to help them.

“Years after this scandal was exposed, far too many people are still waiting for the redress they deserve,” he said.

“The government must now throw whatever resource is needed at these schemes to ensure every outstanding Horizon shortfall claim is settled by the end of this year. Complexity is no longer an excuse for delay.”

Byrne said Fujitsu must “stop sitting on the sidelines”, adding: “It is extraordinary that a company at the heart of the greatest miscarriage of justice in British history has still failed to set out either the scale or the timetable for its contribution to compensation.

“It should make an immediate interim payment, commit to a timetable for meeting its full liability, and help bring this shameful chapter to a close.”

The tech company is negotiating a settlement with the UK government, but has not yet contributed towards the £1.5bn compensation bill for victims, footed by UK taxpayers, even though it admitted it had known since the 1990s that the Horizon system was faulty.

There are three Horizon-related redress schemes for victims: the Horizon shortfall scheme (HSS), the group litigation order and the Horizon convictions redress scheme.

The HSS, the biggest, is administered by the Post Office. Under the scheme, operators with a successful claim can receive a fixed sum of £75,000 or choose to pursue a higher amount.

In March, the business and trade committee found the scheme’s offers for redress were routinely overturned and increased after an appeal.

Last year, the first tranche of findings from the public inquiry into the scandal by the retired judge Sir Wyn Williams found the Post Office and its advisers had in many cases adopted an “unnecessarily adversarial attitude” to those seeking financial redress.

No date has been set for the release of the second and final part of the report, which is expected to focus on the Horizon system’s flaws, the cultures of the Post Office and Fujitsu, and how post office operators came to be wrongfully prosecuted.

The pressure on Fujitsu comes as the company reported on Tuesday that its chair, Hidenori Furuta, resigned after its board became aware of his “woman-related inappropriate conduct”.

Asked about redress for victims of the Horizon scandal, the company said: “We believe it is the right thing to do for Fujitsu to contribute to compensation and, as we have consistently stated, this will be agreed with government after Sir Wyn has published the findings of his inquiry. Our conversations with government regarding our contribution are ongoing.”

A government spokesperson said: “This report recognises the progress that has been made so far in delivering redress but there is clearly more to do.

“Some claims are more complex and take longer to resolve, and we must avoid placing undue pressure on vulnerable claimants. We will continue processing these cases as quickly as possible to end the wait for full and fair redress.”