A former subpostmaster who unearthed a hidden “operational defect” has demanded the Post Office extend the deadline for loss claims to be made through the Post Office Process Review (PPR).
With a week before the door closes on claims, Denis O’Donnell, who ran a branch in Prestatyn, Wales, for decades, has asked for the moratorium as he believes subpostmasters have not been properly alerted to an operational defect he identified.
The PPR scheme is set to close at 11.59pm on 30 September 2026, leaving just a week for former and current subpostmasters to make claims. It was established in the aftermath of the Post Office scandal, aiming to unearth and provide financial redress to subpostmasters for its “products, policies or processes that may have caused financial loss because of the way they were designed or delivered”.
In October last year, O’Donnell alerted Computer Weekly to a Horizon system problem that causes losses, which – through expertise from forensic investigator Ron Warmington – Computer Weekly was able to make public.
O’Donnell had originally informed the Post Office about the problem in 2019, but said he was “fobbed off”. After pressure from Computer Weekly and Warmington, the Post Office finally investigated the issue last year and acknowledged it could cause unexplained losses.
The issue, branded the “part payments” defect, was likely to have seen some customers, for decades, receive extra cash from subpostmasters without realising.
A Horizon screen icon which had two opposite uses, allowing the subpostmaster to both take money and pay money, was at the centre of the issue. When multiple transactions, including in and out payments, are held at the same time in what is known as a “stack”, Horizon could make a payment to the customer but record it as a payment to the branch, therefore creating an instant discrepancy.
“What this means is that potentially substantial amounts of money will have been paid over to unsuspecting customers and charged to subpostmasters,” Warmington told Computer Weekly last year.
The Post Office said: “It is impossible to know the exact impact in the network and we acknowledge there will be subpostmasters who have experienced the issue and not raised it. But we do believe the overall impact is limited. The number of discrepancies in a year attributed to this process is 10 out of 14,000 or 0.07%, where discrepancies have been made known to us via our Review and Dispute button on Horizon.”
In December, the Post Office told Computer Weekly: “We would like to assure your readers that Post Office today has taken this matter seriously and our chief technology officer, chief corporate affairs officer and central operations director met virtually with Mr Warmington and Mr O’Donnell twice. We encourage any current or former postmaster who believes they may have been impacted by this issue to get in touch as they may be eligible for redress through the PPR.”
Read more about O’Donnell’s revelation: Post Office scandal investigator warns public inquiry about Horizon defect at large for years.
But O’Donnell does not believe the Post Office has done enough to encourage subpostmasters to come forward in relation to what Warmington described as a “operational defect”. O’Donnell fears that many subpostmasters will miss out on what they are owed unless the Post Office gives more time for them to make claims for loses caused by the “part payments” defect.
The former subpostmaster himself made a claim in the PPR scheme, which included “part payments” defect losses, but the Post Office made no offer based on claims related to the “part payments” defect.
After O’Donnell posted his displeasure on LinkedIn, he received an apology from the Post Office.
The Post Office wrote: “We are very sorry for this indeed. We recognise that this may have caused further confusion and distress in relation to an issue that has already caused significant distress to you. We are reviewing our processes to understand how this has happened. Please be assured that the PPR team is aware of the ‘part payments’ process issue you have raised. We are actively considering this in relation to your claim (and any others which flag this) and will be in touch again in due course regarding your PPR claim.”
No extension
The Post Office said it will not extend the deadline, adding that people who experienced the “part payments” defect, without understanding it, may have been compensated through the £75,000 fixed sum in the Horizon Shortfall Scheme (HSS).
“For example, if a postmaster had a discrepancy caused by the ‘part payments’ issue but did not understand what had caused it, they may have applied to the HSS,” it said. “The breadth of the definition of a ‘Horizon shortfall’ for the Fixed Sum Offer in HSS means that if someone has a discrepancy that they, or Post Office, can’t explain as something other than a potential issue with a previous version of Horizon, this would be eligible for redress through the HSS.”
HSS was open between 2020 and 2026 and, to date, more than £1bn has been paid through this scheme to 12,630 people.
But O’Donnell said: “We accepted it at face value, that meeting with the Post Office in December, that they were actually going to do what they said. They said they would put it out as part of the PPR claim. If you look to the documents that they sent down advising people how to fill these forms in, there’s no mention of it whatsoever on there.”
Since the PPR opened in May 2025, the Post Office said it has written individual letters to around 36,000 current and former subpostmasters. “While it would not be possible to guarantee that we have reached every single former subpostmaster, we have exercised our best endeavours to do so,” said the Post Office.
A spokesperson said: “We encourage anyone who believes they may have experienced a financial loss as a result of Post Office products, policies or processes which were not designed or delivered properly to submit a request to the Post Office Process Review ahead of the deadline on 30 September, even if they are unsure of the full extent of any losses at this time.”
The Post Office scandal was first exposed by Computer Weekly in 2009, revealing the stories of seven subpostmasters and the problems they suffered due to Horizon accounting software, which led to the most widespread miscarriage of justice in British history (see below timeline of Computer Weekly articles about the scandal since 2009).
