A barrister has heavily criticised senior Post Office staff who he said had defended the Horizon system “out of an almost religious panic”, an inquiry has heard.

Simon Clarke told the Horizon IT inquiry he was “misled and deceived” throughout the scandal by Post Office lawyers Jarnail Singh and Rodric Williams, particularly in the case of jailed subpostmistress Seema Misra.

He described an instruction to shred meeting minutes about Horizon bugs allegedly given by the company’s then-head of security John Scott as a “deliberate back-covering exercise”.

Mr Clarke worked as a barrister for law firm Cartwright King at the time he advised the Post Office – and said he told the company to cease prosecutions after learning that leading Horizon engineer Gareth Jenkins had not disclosed knowledge about bugs in the system.

He criticised the culture at the business during his evidence to the inquiry on Thursday, saying Post Office staff “appeared to work in silos, no one department either communicating meaningfully with, or listening to, the other”.

Mr Clarke said he discussed with managing partner of Cartwright King, Stephen Gelsthorpe, that there was a “sort of back-covering mentality” at the Post Office following a 2013 report from forensic accountants Second Sight – who identified bugs in the system.

The witness said in a statement to the inquiry: “Looking back, I now see what appears to have been three strands of thought within the Post Office on the topic of disclosure.

“The first strand amounted to an article of faith: ‘Horizon is both robust and reliable — there is nothing wrong with it and if Horizon says money is missing, then it is missing’.

A post office van
Simon Clarke criticised the culture at the Post Office during his evidence to the inquiry (James Manning/PA)

“The second strand considered that the cost of providing disclosure was prohibitive and should always be discouraged.

“The third strand, I felt, arose out of an almost religious panic: ‘Horizon must not be seen to have been impugned’.”

During an exchange with chairman Sir Wyn Williams, Mr Clarke told the inquiry it was now his view that the prosecution file in the case of Mrs Misra was “deliberately withheld” from him by the Post Office.

Mrs Misra, who began running a branch in West Byfleet, Surrey, in 2005, was handed a 15-month prison sentence while eight weeks pregnant in November 2010 after being accused of stealing £74,000.

Sir Wyn asked Mr Clarke: “And is it your view, let me ask you the direct question, that the (prosecution) file whether in electronic or paper form, was deliberately withheld from you?”

Mr Clarke replied: “That is now my view.”

Sir Wyn continued: “And is that now your view… having no doubt listen to parts of the inquiry and looked at various documents? Or was that a view which you formed earlier than that?”

The barrister said: “I watched Rodric Williams, I watched Jarnail Singh twice, I’ve watched (Cartwright King solicitor) Martin Smith and I watched (Cartwright King barrister) Harry Bowyer, and as a result of that, combined with the documents that I’ve seen in this process, that crystallises my view that I was misled and deceived – in particular in reference to the sight of the Seema Misra file… but also in general.”

The chairman then said: “You are asserting that you were misled deliberately in the Seema Misra case?”

Mr Clarke responded: “That’s my belief, yes.”

Sir Wyn continued: “But you also say that you have a belief that you were misled on a wider basis?”

Mr Clarke said: “Yes. Post Office repeated the protestations that since day dot there was nothing wrong with Horizon when they clearly knew that there were issues with Horizon.”

Addressing the instruction allegedly given by Mr Scott to shred minutes of meetings about Horizon bugs, Mr Clarke said it was not due to incompetence.

He said: “This instruction was not, in my then view, an act of incompetence on the part of John Scott or the Post Office — he was a former police officer with experience of the criminal investigative process.”

Counsel to the inquiry Julian Blake asked: “Was John Scott seen as a lone wolf or someone who was working with others in that respect?”

Mr Clarke replied: “The impression I got from within Post Office and from within Cartwright King was that he was regarded as being a bit of a power unto himself.”

After further questioning, the barrister added: “My understanding was this wasn’t a Post Office policy or instruction, this was John Scott on a frolic of his own.”

Questioned on whether senior Post Office lawyer Jarnail Singh was concerned about Mr Scott’s “shredding” advice, Mr Clarke said: “Yes. I think the proper word is frightened.”

Addressing the alleged shredding in his witness statement, Mr Clarke said: “I recall that my conversations with (senior Cartwright King staff) would have been conducted in surprise and shock — we had just been informed that our client, or some of their staff, were potentially acting criminally by attempting to pervert the course of justice.

“We considered it essential that the Post Office immediately be advised both of the unlawful conduct and the underlying law and duties on them to prevent such conduct.”

He added: “We were at a loss to understand why John Scott would give such an instruction or why others within the Post Office did not wish to minute the weekly conference calls.

“We perceived the shortcomings referred to as being a complete lack of judgment and understanding on the part of some, to fully appreciate the importance of retaining material for disclosure, and in respect of others, a deliberate back-covering exercise.

“As to whom we were referring to, the former category included Jarnail Singh, and his criminal law team, and some other department representatives attending the weekly calls.

“In the latter category we included John Scott and his security and investigative staff, all of whom should, and likely did, know better.”