You would think that the Post Office has learnt its lessons from the Horizon IT Scandal. And of course it would have taken extra care to ensure that the victims of the UK’s most widespread miscarriage of justice are not further harmed by their actions in dealing with the aftermath. Not so, judging by the Information Commissioner’s Office (ICO) announcement on Tuesday.
The ICO has issued a reprimand to Post Office Limited following an ‘entirely preventable’ data breach which resulted in the unauthorised disclosure of personal data belonging to hundreds of postmasters who were the victims of the Horizon IT scandal. The breach occurred when the Post Office’s communications team mistakenly published an unredacted version of a legal settlement document on its corporate website. The document contained the names, home addresses and postmaster status of 502 people who were part of group litigation against the organisation. The document remained publicly accessible for almost two months in 2024, before being removed following notification from an external law firm.
During its investigation, the ICO found that the Post Office failed to implement appropriate technical and organisational measures to protect people’s personal data. There was a lack of documented policies or quality assurance processes for publishing documents on the Post Office website, as well as insufficient staff training, with no specific guidance on information sensitivity or publishing practices.
In the ‘gold old days’ such a data breach would have attracted a substantial fine; especially considering the impact on the victims described by their lawyers (‘the shock and anxiety of this incident cannot help but compound all of the adverse harms suffered by our clients as a result of the wider Horizon scandal’.) Remember when the ICO fined the Cabinet Office £500,000 for disclosing postal addresses of the 2020 New Year Honours recipients online?
But we are in a new age of GDPR ‘enforcement’! The ICO says it had initially considered imposing a fine of up to £1.094 million on the Post Office Limited. However, it did not consider that the data protection infringements identified reached the threshold of ‘egregious’ under its public sector approach, and a reprimand has been issued instead. This approach, which was extended recently after a two year trial, ‘prioritises early engagement and other enforcement tools such as warnings, reprimands, and enforcement notices, while issuing fines for only the most egregious breaches in the public sector’ so says the ICO. Not everyone agrees. The law firm, Handley Gill, has just published an analysis of the ICO’s public sector approach trial and the new version of it, essentially concluding that reprimands unaccompanied by enforcement notices won’t achieve the stated objective of driving up data protection standards in the public sector.
The ICO highlights the following key lessons from this reprimand:
- Establish clear publication protocols: Sensitive documents should go through a formal review and approval process before being published online. A multi-step sign-off process can help prevent errors.
- Understand the data you handle: Every team, especially those handling public-facing content, must be trained to recognise personal information and assess its sensitivity in context. This includes understanding the reputational and emotional impact of disclosure.
- Centralise and classify documents: Use secure, shared repositories with clear access controls and classification labels. Avoid reliance on personal storage systems such as OneDrive and Google Drive.
- Define roles and responsibilities: Ensure that everyone involved in publishing content understands their role and the checks required before publication.
- Tailor training to the task: General data protection training is not enough. Teams need specific guidance on publishing protocols, data classification, and risk awareness.
This and other data protection developments will be discussed in detail on our forthcoming GDPR Update workshop. The new (2nd) edition of the UK GDPR Handbook has been published. It contains all the changes made by the Data (Use and Access) Act 2025.










