Voice of the Postmaster (VotP), which was set up to campaign for current staff, alleges the discredited IT software is still generating mysterious missing money.

Marlene Wood, postmistress at Comrie Crieff Post Office in Perthshire, alleges the apparent shortfalls she has been facing are partly linked to Horizon and are eating into her profits.

The 53-year-old, who has been in charge of the branch for more than four years, told Sky News: "My business is failing. I will go under in part due to the discrepancies that I pay back.

"There is no computer system that is fail-safe. There continues to be bugs."

Ms Wood claimed there was one discrepancy of a couple of hundred pounds.

She said: "I spent the night going through the safe, transactions, notes and couldn't find anything.

"I went to bed and woke up, redeclared my cash amount and there was no discrepancy. It had vanished.

"I am not saying Horizon is to blame for everything but not to the degree that you go to bed and it can magically disappear."

Ms Wood, who said she is emotionally distressed, estimates she is around £2,000 in the red and is facing losing her livelihood.

She also said her "marriage is gone" and has had to borrow money from her mother.

Ms Wood added: "If it does go under, I am going to have nowhere to live as the house is above the Post Office.

"I will be sleeping on my mum's couch at the age of 53 with no job, no credit rating and owing, potentially, thousands of pounds. That's the reality of having a Post Office."

In response, Post Office chiefs told Sky News it was "very sorry" to learn of the concerns.

A spokesperson said: "We are very sorry to hear of the experience our postmistress for Comrie Crieff is having.

"Our area manager has visited her to understand the issues and talk through the support that is available which could make a difference to her situation, and we are following this up."

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It comes after Japanese technology firm Fujitsu said it plans to compensate sub-postmasters wronged in the original Horizon scandal dating back decades.

The multinational company - which developed the Horizon system - is in the spotlight after TV drama Mr Bates Vs The Post Office renewed public interest in the issue and sparked outrage.

Hundreds of sub-postmasters and sub-postmistresses were prosecuted over claims they were stealing from the Post Office - but the missing money was actually due to errors in the IT software.

A different version of the Horizon software is used today but Voice of the Postmaster claims problems persist with "not a postmaster in the country" unaffected.

Sara Barlow, secretary of VotP committee, told Sky News: "Horizon is not the robust system that we'd like to think in 2024.

"Obviously, there's human error but we are all experienced enough to find where we've made an error and rectify it.

"There are plenty of times where things just don't add up, things don't make sense, and we don't know where the shortfall has come from."

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Ms Barlow, who runs a branch herself, alleges Horizon "absolutely" is to blame.

She said: "There are plenty of times where they can't account for where the mistakes are coming from, they've checked CCTV, action logs.

"I'm sure the system has improved from 2015 but it is still happening. It is still having issues. There are still plenty of people who are having sleepless nights."

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The Post Office said there have been several versions of Horizon since its introduction in 1999.

A spokesperson added: "And the current version of the system, introduced from 2017, was found in the group litigation to be robust, relative to comparable systems.

"But we are not at all complacent about that and we continue to work with our postmasters to identify and invest in improvements.

"Current postmasters who have concerns about today's Horizon system are encouraged to raise these with us - including directly with their area manager - so that we can help."