The RMT union has instructed its members to occupy the line’s ships following national press reports that P&O’s owner, Dubai-based global logistics and trading firm DP World, planned to replace all of its UK seafarers with overseas labour.

TTG has approached P&O Ferries and DP World for comment. The dispute doesn’t concern P&O Cruises’ operations or staff.

General Secretary Mick Lynch said: "We are deeply disturbed by growing speculation that the company [P&O Ferries] are today planning to sack hundreds of UK seafarers and replace them with foreign labour.

"We have instructed our members to remain onboard and are demanding our members across P&O’s UK operations are protected and that the secretary of state intervenes to save UK seafarers from the dole queue.”

On Thursday morning, P&O Ferries said it had suspended operations and discharged all passengers and cargo ahead of a "major announcement" it said would "secure the long-term viability" of the firm.

Hull MP Karl Turner tweeted a copy of an internal statement circulated to staff on Thursday morning (17 March), adding he was in touch with unions about the situation, noting the impact for crews and their families.

In the statement, tweeted by Turner, P&O Ferries said: “We will be making a major company announcement today which, with the support of our shareholder DP World, will secure the long-term viability of P&O Ferries. To facilitate this announcement all our vessels have been asked to discharge their passengers and cargo and standby for further instructions.

"That means we’re expecting all our ports to experience serious disruption today so please bear with us and we will give further information in an all-colleague announcement later today. If you’re in a customer-facing role further information with follow separately on how we would like you to work with our customers. Thank you for your patience and support.”