The scandal, involving problematic technology, occurred during the period when the Big Four firms audited the Post Office. EY, the external auditor for the Post Office from 1986 to 2018, oversaw the roll-out of the Horizon technology. PwC succeeded EY as the auditor in 2018.

With the separation of the Royal Mail and the Post Office in 2012, five individuals from EY and PwC collectively signed off the Post Office’s accounts. EY has expressed its commitment to cooperate fully with the inquiry, while PwC has refrained from commenting on the matter, The Times reports.

The Williams Inquiry, expected to announce its final list of individuals to be questioned in phases five and six in the coming weeks, is closely monitored by the Financial Reporting Council (FRC). Although the FRC lacks direct oversight of the Post Office as a government-owned entity, it can intervene in situations deemed to be in the public interest.

Auditors, responsible not only for verifying financial records but also assessing the strength of an organisation’s systems, play a crucial role in ensuring accurate corporate accounts. This involves a comprehensive understanding of an organization’s IT and information systems to validate financial accuracy.

The limited duration auditors are required to retain audit records – only six years – poses a potential obstacle as EY may lack relevant paperwork when called to the inquiry in the summer.