The chair of the Post Office Inquiry has threatened that anyone responsible for more disclosure failings will be summoned to explain themselves in person.

The statutory inquiry was halted last week after a last-minute admission from the Post Office that documents relevant to that day’s witness were yet to be disclosed.

The witness, former Fujitsu engineer Gareth Jenkins, was due to give evidence over two days about how former Post Office workers were investigated and subsequently prosecuted on the basis of the faulty Horizon IT system. He will not now be able to appear until after the summer.

Inquiry chair Sir Wyn Williams has issued formal direction to the Post Office and its lawyers requiring them to supply documents being produced by the ongoing remediation exercise.

Post Office Limited group general counsel Ben Foat accepted last week that the e-disclosure process had been too ‘mechanical’ despite dozens of in-house and external lawyers being involved.

Williams said the request for documents was about more than just devising search terms and instead required a ‘common sense’ approach and understanding of the context in which the Post Office scandal has developed.

He said: ‘I am dissatisfied by the approach that has been taken by the Post Office; in my view, their approach demonstrates a lack of clear thinking about the disclosure obligations owed to the Inquiry with which the Post Office must comply and the means by which their obligations can be fulfilled.’

Williams suggested the postponement of Jenkins’ appearance and the late disclosure of documents had the potential to jeopardise the smooth running of the inquiry. He added: ‘It wastes public funds, it delays the provision of answers to those who were affected and delays the learning of lessons through the recommendations that I will in due course make.’

In the current phase of the inquiry, the chair has ruled that for all witnesses who are due to give oral evidence up to and including 28 July, documents must be provided no later than two clear working days ahead.

He added that the Post Office could not attempt to shift the blame onto third parties who have been instructed to carry out document checks.

While disclosure obligations fall on all document providers, the Post Office’s disclosure obligations in this Inquiry are further heightened. This makes the errors highlighted by Mr Foat’s evidence all the more inexcusable and unacceptable,' he said. ‘I will not hesitate to continue to call those responsible to give evidence to the Inquiry to account for any failings.’

This week, the inquiry will hear from former Post Office heads of security, the former head of its criminal law team and its former senior debt recovery manager.