Hundreds of people have marched in protest at ports after almost 800 seafarers were sacked without notice earlier this month. Demonstrations took place in Liverpool, Dover and Hull, as calls grew for a P&O Ferries boss to quit. Crowds walked with banners and placards, chanting “P&O, shame on you” at rallies on Saturday. The demonstrations come after a ship operated by the ferry firm was detained for being “unfit to sail”. The European Causeway has been held at the port of Larne in Northern Ireland. The vessel is one of two that run from Larne and Cairnryan, Scotland. However, sailings remain suspended after the company’s decision to sack 800 seafarers and replace them with cheaper agency workers. The Maritime and Coastguard Agency (MCA) said the ship had been detained due to “failures on crew familiarisation, vessel documentation and crew training”, while the transport secretary, Grant Shapps, said he would not compromise the safety of P&O Ferries vessels. The MCA said: “We can confirm that the European Causeway has been detained in Larne. It has been detained due to failures on crew familiarisation, vessel documentation and crew training. “The vessel will remain under detention until all these issues are resolved by P&O Ferries. Only then will it be reinspected.” The MCA confirmed there were no passengers or freight on board the European Causeway when it was detained. The vessel first entered service in 2000, replacing the Pride of Rathlin, according to the P&O Ferries website. Meanwhile, Shapps tweeted: “Following my instruction to inspect all P&O vessels prior to entering back into service, the MCA-Media has detained a ship for being unfit to sail. “I will not compromise the safety of these vessels and P&O will not be able to rush inexperienced crew through training.” P&O Ferries informed customers on social media that services between Larne and Cairnryan were suspended. The company said: “It is no longer possible for us to arrange travel via an alternative operator on this route. For essential travel, customers are advised to seek alternatives themselves.” The RMT’s general secretary, Mick Lynch, called for the government to seize P&O’s entire fleet of ships, and for crew who were sacked without being consulted or given any notice to be reinstated. “The seizing of the European Causeway by the MCA tonight shows that the gangster capitalist outfit P&O are not fit and proper to run a safe service after the jobs massacre,” he said. “This mob should be barred, their ships impounded and the sacked crews reinstated to get these crucial ferry routes back running safely.” The shadow transport secretary, Louise Haigh, called for the sacked workers to be reinstated and for P&O Ferries’ chief executive, Peter Hebblethwaite, to be “barred” as a director. She wrote on Twitter: “The trained, experienced, loyal crew should be reinstated. And the chief executive should be barred as a director. The shameful misconduct of P&O Ferries has ruined livelihoods, and is harming the UK’s key shipping routes.” Labour has written to the business secretary, Kwasi Kwarteng, asking whether the government will seek the removal of Hebblethwaite as a director under the Company Directors Disqualification Act 1986, PA Media reported. In a letter, the party accused the government of “sitting on their hands” instead of taking action to hold P&O to account, adding that the “toothless response risks giving the green light to exploitation”. Boris Johnson has also backed Shapps’s call for Hebblethwaite to step down.