Edward Henry KC and Flora Page, who represent former sub-postmasters Lee Castleton and Seema Misra, among others, in the Post Office scandal, made the remarks in a closing statement for the Horizon inquiry.

Writing for the legal firm Hodge Jones & Allen's submission in Phase 4 of the inquiry, he accused Post Office lawyers and investigators of conspiracy to pervert the course of justice with Fujitsu staff in the litigation with Mr Castleton.

The former sub-postmaster owned a branch in Marine Drive, Bridlington, east Yorkshire, and was bankrupted by a lawsuit against the Post Office after a shortfall of £25,000 was flagged by his Horizon IT system.

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Mr Henry alleged that the Post Office's reliance upon Mr Castleton's cash accounts during litigation against him while "knowing there was expert evidence as to its unreliability, was a course of conduct which had a tendency to pervert the course of justice".

He added: "It allowed POL to obtain judgment for a debt, and the consequent costs order, without producing reliable evidence that the debt was owed."

The lawyer then said: "There is evidence that this course of conduct was also maliciously intended to pervert the course of justice, because the POL group either knew that the Marine Drive cash accounts may not have been reliable, or they closed their eyes to that knowledge.

"The motive for the course of conduct may have been to protect POL, or their own jobs, and the natural consequence of the course of conduct may not have been desired as such, but that does not mean it was not intended.

"Mr Castleton's destruction may have been seen as unfortunate collateral damage in order to protect Horizon at all cost."

Castleton bankrupted by litigation

The lawyer made his remarks based on evidence from the litigation against Alan Bates and Phase 1 of the Horizon Inquiry.

Within a year of buying the Marine Drive branch in 2003, Mr Castleton's computer system showed a £25,000 shortfall.

He had called the Post Office's helpline 91 times as he believed the Horizon IT system was at fault, but was taken to court by the firm in 2007.

The former sub-postmaster had to represent himself as he could not afford a lawyer, and was ordered to repay the money and pay costs of £321,000, which bankrupted him.

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Fujitsu 'lacked knowledge' of Horizon use

Meanwhile, Fujitsu alleged in their closing remarks that they were unaware of how the Post Office would use information from the Horizon systems against sub-postmasters.

In page nine of their submission, the firm said they accept "that in some cases, although Fujitsu provided no particular support to a prosecution or civil claim... it is nonetheless clear that information derived from the Horizon system was instrumental to a number of the wrongful prosecutions and civil proceedings pursued against sub-postmasters".

They then alleged "that, once support was provided by Fujitsu to Post Office in a particular case... Fujitsu lacked control, and typically lacked knowledge, as to how that evidence would be deployed by Post Office in that case, or in any subsequent cases".

The newest remarks are at odds with Fujitsu's European boss Paul Patterson's statement to the select committee in January, where he admitted staff knew of bugs, errors and defects in the Horizon IT system as far back as 1999.

Mr Patterson also said in an earlier committee appearance that the technology giant had a "moral obligation" to contribute to the compensation scheme for those whose lives were ruined by the scandal.

Sky News has contacted the Post Office for comment.