The ousted chief executive of software firm Torex Retail has threatened to sue the company for £30m, claiming unlawful dismissal and warning of action under whistleblowing laws.

Neil Mitchell’s employment was terminated earlier this month. At the time Torex, which produces software for the retail and hospitality industries, declined to comment on the reason for his departure.

But Mitchell has now written to interim Torex chair Steve Marshall, warning that he intends to launch a £5.4m constructive dismissal claim within four weeks, saying that he had been unlawfully dismissed after being suspended, in breach of his contractual rights, the Financial Times reported.

Mitchell told Marshall he had not resigned. He also threatened to claim a further £25m in unlimited damages under the Public Interest Disclosure Act, which was drawn up to protect whistleblowers.

The whistleblowing claim relates to a dossier passed by Mitchell to the Serious Fraud Office in January. It contained details of alleged fraud, insider trading and money laundering at Torex.

Mitchell was suspended in January after the firm posted a heavy profit warning, only eight days after announcing new contract wins. The company’s shares were suspended and the company is under investigation by the London Stock Exchange and the Financial Services Authority as well as the Serious Fraud Office.

Torex, which has a net debt of £300m, is currently up for sale.