P&O Ferries has sacked seven of the agency workers it brought in to replace nearly 800 crew members who were made redundant in March.

The UK company, owned by Dubai’s DP World, confirmed that the seafarers were dismissed after returning to a ferry in breach of guidelines on alcohol consumption.

P&O Ferries added: “The safety of our passengers and crew is our foremost priority and we continue to operate a zero-tolerance policy towards drinking whilst on duty.”

The company hit the headlines last month when it sacked all its UK seafarers with no notice, in order to bring in cheaper casual labour.

Another protest march against the sackings was held in Dover on Tuesday.

Darren Procter, from the RMT union, told the BBC the latest incident was “absolutely scandalous”.

He said: “They could end this today by saying to the RMT…: ‘We’ve made a mistake, we’ve compromised safety, we’ve jeopardised our reputation in the local community, and we want to come back to you.’”

P&O’s Dover to Calais ferry fleet is still awaiting safety clearance from the Maritime and Coastguard Agency.

The shipowner claimed it had to change its business model because it was losing huge sums of money each year.

P&O had hoped to resume sailings over Easter, but two of its ropaxes on the Dover-Calais route failed safety inspections.

John Lansdown, a former ferry chef who was sacked and is suing P&O for unfair dismissal, racial discrimination and harassment, said he was “sickened and distressed” over the way he and his colleagues were treated.

He said: “We’re on day 34 now and there appears to be no end in sight to the chaos that we’re seeing inflicted upon roads in Kent, and many local businesses, as a result of the actions of P&O ferries.”