Sources inside HMCTS say judges in civil, family and tribunal courts will have ruled on cases without seeing all the evidence.

The internal report, obtained by the BBC, said HMCTS never fully investigated the scale of the data corruption and decided not to inform judges or lawyers because it would be “more likely to cause more harm than good”.

HMCTS insists its probe found no proof that “any case outcomes were affected” but Sir James Munby, former head of the High Court’s family division, called the situation “shocking” and “a scandal”.

The fault lay in case-management software, known as Judicial Case Manager, MyHMCTS or CCD, which is used across courts and tribunals to handle evidence and track cases.

The Beeb found documents proving it hid key data such as medical records and contact details from case files. The Social Security and Child Support Tribunal was worst hit, but bugs also affected systems used in family, divorce, employment, civil money claims and probate courts.

Sources compared the affair to the Horizon Post Office scandal, accusing senior management of a “culture of cover-ups” and of ignoring repeated IT staff warnings since 2019. One said bosses were more concerned about hiding risks from the public than fixing them.

A March 2024 HMCTS briefing rated the risk to proceedings as “high” and the likelihood of adverse court outcomes as “very likely”, but its review covered only three months of SSCS cases. Of 609 cases with possible issues, just 109 were investigated and one was deemed to have a “potentially significant impact”. Management then declared the risk low and halted checks.

A whistleblower complaint triggered a deeper probe led by a senior Prison Service IT official, whose November 2024 report found “large-scale” breaches that should have been fixed immediately, yet HMCTS had taken years to act. The true extent of corruption and its impact on rulings remained unknown.

Separate sources say a different flaw wiped more than 4,000 documents from hundreds of public family law cases, including child protection hearings. The bug, found in 2023, has been fixed, but no inquiry was carried out into possible harm.

Liberal Democrat shadow attorney general Ben Maguire MP called the revelations “shocking and deeply concerning” and demanded “a full, independent investigation now to uncover any miscarriages of justice”.

Former Conservative justice secretary Alex Chalk described the matter as “unbelievably serious” and said he was “incredibly troubled” that it had never been brought to his attention, calling for a government-level probe and a “root-and-branch overhaul” of HMCTS governance.