The tech entrepreneur Mike Lynch is counter-suing Hewlett-Packard over allegations that he mismanaged the software firm Autonomy that he sold to HP in 2011.
The announcement on Tuesday follows a day after HP launched a case seeking $5.1bn (£3.4bn) in damages, following years of rancour between the firms and a huge devaluation of Autonomy in the wake of the purchase.
The statement from Lynch’s team said: "The former management of Autonomy announces today they will file claims against HP for loss and damage caused by false and negligent statements made against them by HP on 20 November 2012 and in HP’s subsequent smear campaign.
"Former Autonomy CEO Mike Lynch’s claims, which is likely to be in excess of £100 million, will be filed in the UK."
Formed in 1996, Autonomy was sold to HP for $11.1bn in 2011, but had $8.8bn wiped off its value by HP in November 2012 amid allegations of "serious" accounting problems, claimed by HP to be responsible for $5bn worth of the revaluation.
Lynch had been fired from the company earlier that May as an internal investigation began, but has since maintained the problems are due to HP’s mismanagement.
Following that the dispute has been fought over by lawyers and regulators on both sides of the Atlantic, most recently in a probe by the Serious Fraud Office that was dropped in the UK earlier this year.
Speaking about the current case, an HP spokesman said: "HP can confirm that, on March 30, a claim form was filed against Michael Lynch and [former Autonomy CFO] Sushovan Hussain alleging they engaged in fraudulent activities while executives at Autonomy.
"HP will not comment further until the proceedings have been served on the defendants."
