At a demonstration in Hull on Tuesday, the Rail, Maritime and Transport Workers union’s National Secretary Darren Procter said they would keep up the pressure on the company and the government over the sacking of 800 staff last month, including 82 ratings and officers from the Pride of Hull.

Nearly three weeks on only two out of the 11 ferries operated by P&O have resumed sailings. Pride of Hull remains in Rotterdam and passengers have been told that she won’t be sailing until April 23.

Meanwhile in Dover where there have been queues due to the shortage of cross-Channel ferries, P&O Ferries services are not expected to resume until April 19.

Pride of Hull isn't expected to resume service until April 23

Mr Procter said blockades would take place at ports “if it’s Easter or summer” if crews were not reinstated. And he insisted there would be an accident on board one of the ferries, as a result of new crews being unfamiliar with the vessels.

“I can confidently predict there will be blood on the hands of P&O and their directors”, he told The Yorkshire Post.

He said although Transport Secretary Grant Shapps was telling port operators to do due diligence to ensure crews were on the minimum wage, the union is insisting on collective bargaining, safe roster patterns and pensions for workers. He said agency crews were working 12 hours a day, seven days a week for two months at a time, and he’d heard Indian seafarers had been bought in on four months contracts.

Hull East MP Karl Turner told the gathering of around 50 people at King George Dock that fatigue had been the cause of the sinking of the Herald of Free Enterprise when it left Zeebrugge with the bow doors open in 1983. The MP said the new working practices would not give staff proper rest breaks, adding: “They only wake up when there has been a terrible tragedy.”

Protests continue today at Liverpool and tomorrow at Cairnryan.

P&O Ferries: Unions threaten port blockades if sacked crews are not reinstated