Armed French police have begun patrols on cross-Channel ferries in a bid to prevent terrorist attacks, reports the BBC.
The scheme started on Monday, but with no agreement yet in place for French police to patrol vessels in UK waters, they arrived by helicopter and boarded a ferry as it approached France.
The two governments are in talks about French officers patrolling for full crossings, France's marine police said.
The Home Office said security plans were under "constant review".
French authorities told the BBC no timeline had been set for an agreement to be reached.
Speaking to the AFP news agency, French marine police spokesman Lieutenant Pierre-Joachim Antona said a "permanent unit" had been deployed since Monday to carry out high-visibility patrols on passenger ferries.
"The marine gendarmes will carry out patrols, which will be random but regular, with the aim of securing these vessels against the terrorist threat," he said.
The first patrol took place on Monday, when three French sea marshals arrived on the Brittany Ferries vessel Mont St Michel by helicopter.
A Brittany Ferries spokesman said the vessel left Portsmouth for Caen in France at 14:45 BST and, in a "pre-scheduled security exercise", the marshals were flown on to the boat at 17:30.
"They then proceeded to patrol the bridge and passenger areas of the vessel," he said.
He added: "Passengers were informed via announcements in English and French before the exercise took place.
"Access to outside decks was not allowed at the time of the helicopter's arrival."