Hewlett-Packard disputed with its auditors whether $5bn (£4bn) of a writedown in value of the software firm Autonomy could be blamed on fraud allegedly engineered by the tech entrepreneur Mike Lynch, according to documents filed to a US court. Lynch, a billionaire founder once lauded as the UK’s answer to Bill Gates, was extradited to the US in May to face criminal fraud charges over allegations that he duped HP into overpaying when it struck an $11bn deal for Autonomy in 2011. HP subsequently took an $8.8bn writedown in the firm’s value after discovering “serious accounting improprieties” at Autonomy, blaming Lynch for perpetrating a $5bn fraud, an accusation he denies. In 2022, Lynch lost a six-year civil fraud case in the UK, with the high court judge ruling that HP had been induced into overpaying for the takeover because of fraud perpetrated by Lynch and Autonomy’s former finance director Sushovan Hussain, who is in jail in the US after being found guilty of fraud relating to the same deal. However, legal documents filed by Lynch’s lawyers to a court in California and made public on Wednesday appear to show disagreement between HP and its external auditors, EY, over whether a $5bn figure could be attributed to fraud. The filing contains dozens of exhibits that Lynch’s lawyers have legally obtained in building a defence case, which were not available at the time of Hussain’s trial. These include email communications between parties involved including HP, EY, Autonomy’s former auditor Deloitte and PwC, which carried out an internal investigation into the fraud allegations for HP. The communications show that EY did not back HP’s claim that the “majority” of the writedown was because of fraud, and the accountancy firm again did not support the use of the language in the software company’s annual report in 2012. In December of that year, one of HP’s accountants also said in an email that “it would be extremely difficult to calculate the portion of the impairment that relates to accounting improprieties/misrepresentations”. The documents also show that the US Securities and Exchange Commission (SEC) looked into HP’s claim that more than $5bn of the Autonomy writedown was because of fraud. The court filing argues that Lynch has been caught up in a “blame game” over the failed integration and performance of Autonomy under HP ownership. “This dispute between HP and its auditor regarding HP’s statements surrounding the writedown is directly relevant to Dr Lynch’s defence to the government’s claim that he misled the public following HP’s allegations,” the lawyers said. In the court filing, Lynch’s lawyers are seeking a court order to subpoena further communications and evidence from HP, EY, PwC and Deloitte. Lynch has been confined to an address in San Francisco with a 24-hour security detail, which he has to pay for, after landing in the US after a court ruling that “defendants with such vast wealth present a substantial risk of flight”. The entrepreneur, who was awarded an OBE for services to enterprise and was an adviser to David Cameron when he was prime minister, is a founder and investor in the British cybersecurity firm Darktrace. If Lynch is convicted in the US he could face up to 20 years in prison. HP and EY were contacted for comment.