UK authorities holds P&O ship in Northern Ireland over safety fears after mass sackings

British authorities detained a P&O Ferries vessel in Northern Ireland saying it was "unfit to sail," in the latest fallout from the firm's mass staff sackings.

The European Causeway vessel has been held in Larne, north of Belfast, due to "failures on crew familiarisation, vessel documentation and crew training", Britain's Maritime and Coastguard Agency (MCA) said.

Transport Secretary Grant Shapps ordered inspections of all P&O vessels after the company controversially sacked almost 800 seafarers on March 17 to replace them with cheaper agency workers.

"I will not compromise the safety of these vessels and P&O will not be able to rush inexperienced crew through training," Shapps said on Twitter as he flagged the MCA's enforcement action.

A spokesperson for the agency said the ship will remain detained until the issues around its documentation and crew training are resolved.

"Only then will it be reinspected," the spokesperson added.

P&O Ferries suspended operations to and from Britain across the Channel and Irish and North Seas when it announced the plans to replace its workforce with agency crews paid far below the UK minimum wage.

The British government said Friday that it would force the firm to do a U-turn over the heavily criticised move.

Shapps also called for its chief executive Peter Hebblethwaite to resign, a day after he told a parliamentary hearing that the company chose not to consult unions on the move, as it was legally obliged to do.

Protests over P&O Ferries's actions are expected to take place in UK port cities including Liverpool, Hull and Dover on Saturday.