As many as a quarter of the staff at Autonomy quit the UK software group soon after its acquisition by HP, former employees said, with one likening the US computer maker’s internal procedures to “being waterboarded” almost daily.

The $10.3bn deal in August was the biggest acquisition of a European IT company and was heralded by Léo Apotheker, HP’s chief executive at the time, as a chance for HP to gain leadership in searching unstructured data with Autonomy’s “well-regarded management team and talented, dedicated employees”.

Citing weak sales and poor management at the subsidiary, Meg Whitman, HP’s current chief executive, on Wednesday announced the departure of Mike Lynch, Autonomy’s founder, amid a shake-up to cut 27,000 jobs and restructure the company’s computer business.