Brittany Ferries has put in place extra security measures across its fleet, including on boats travelling to and from Portsmouth.
The company said a comprehensive and independent review of security was carried out over the last six months.
As part of this specialist security personnel will now travel on some sailings.
Extra bag checks will also start as passengers leave car decks and head to public spaces.
Christophe Mathieu, chief executive of Brittany Ferries, said: ‘These measures are a prudent step for a responsible ferry operator and I must be clear that they are not in response to any threat.
‘We work very closely with the authorities in both France and the UK and security is already our highest priority.
‘But I hope this significant investment will reassure passengers that we are taking all reasonable steps to ensure their journey with Brittany Ferries continues to be as safe as it is enjoyable.’
As previously reported in The News, last summer Brittany Ferries introduced cross-channel ‘sea marshal’ patrols on its ships.Armed French military personnel were originally winched on board by helicopter in international waters, in a partnership the company had with the French government.
But since last autumn they have been travelling from port-to-port, including within UK waters. They board, patrol the ferry and disembark on foot.
The new measures are being implemented ahead of the summer holidays and will run alongside the on-going sea marshal patrols.
Councillor Donna Jones, leader of Portsmouth City council, welcomed the move.
She said: ‘Portsmouth International Port will work in co-operation with Brittany Ferries as the safety and security of all passengers remains a high priority.
‘This precautionary measure can only help to deter any incidents occurring during the crossings between the mainland and Portsmouth.
‘The port and Portsmouth City Council both have a very close relationship with Brittany Ferries and we understand these arrangements are only precautionary.’
Portsmouth South Labour MP Stephen Morgan added: ‘It is for Brittany Ferries to determine what steps it should take for the security of its passengers.
‘But my personal view is if these measures, introduced as a result of an independent review, help assure passengers and staff, then they are the right thing to do.’