P&O Ferries will not face criminal proceedings for firing almost 800 workers earlier this year, the Insolvency Service has determined.

The company caused outrage and was hauled in front of MPs to answer questions in March when it sacked hundreds of workers without notice.

Business Secretary Kwasi Kwarteng asked the Insolvency Service to investigate whether any offences had been committed.

But the government agency said in a statement it had determined there was "no realistic prospect of a conviction".

A spokesperson said: "After a full and robust criminal investigation into the circumstances surrounding the employees who were made redundant by P&O Ferries, we have concluded that we will not commence criminal proceedings."

A civil investigation is ongoing.

Nautilus International, a union representing maritime professionals, said the Insolvency Service's decision will be a blow to the "discarded" workers.

General secretary Mark Dickinson said: "This is a deeply disappointing decision and will be met with frustration and anger by the 786 seafarers and their families who were so cruelly discarded by P&O Ferries.

"Only one day after P&O Ferries parent company announced record profits, making the company's claims on operational sustainability questionable, we are further let down by a system that fails to punish apparent criminal corporatism.

"The message is clear, P&O Ferries must be held properly accountable for their disgraceful actions and we will continue the campaign to ensure that the CEO and his fellow directors are held to account and to make certain this can never happen again."

During hearings in Parliament the business admitted it had broken the law that would have forced them to give notice of the firings.

At the time bosses said this was because no unions would have accepted the new proposals.

A government spokesperson told the BBC: "In sacking 800 dedicated staff on the spot, P&O Ferries not only acted callously but failed to uphold the high standards we expect of British businesses.

"Given their appalling behaviour, it's very disappointing that the company will not face criminal proceedings."

It comes after transport secretary warned the company would have "no choice in law" but to pay crew members the minimum wage after the firm's owner reported record profits following the mass sacking.

Issuing the ultimatum, Grant Shapps said the company will be forced to back down and so should make the change now, before repeating his demand for P&O boss Peter Hebblethwaite to quit.