Armed guards could be stationed on ferries sailing from France to Portsmouth as part of heightened security arrangements.
Talks about a proposal to deploy French personnel to patrol on boats are understood to be ongoing between the two country’s governments.
It is believed the plan involves placing marshals on French-flagged vessels departing from ports in France.
Discussions are likely to cover the questions of how the measures would work, and what powers the guards would have, when ferries cross into UK territorial waters.
The development follows a spate of terrorist attacks in Europe, including the deadly assaults in Paris and Nice. Last month there were long delays on the approach to Dover in Kent after extra French security checks were put in place.
In an exercise on Monday, armed personnel arrived on board a ferry travelling from Portsmouth to Caen.
Half-way through the crossing, around three hours before the ship’s scheduled arrival in France, three French sea marshals wearing full military kit landed on the ship by helicopter.
A Home Office spokesman said: ‘We work extremely closely with our French counterparts on matters related to security and counter-terrorism.’
David Balston, of the UK Chamber of Shipping, said: ‘Security levels are continually reviewed and there is a constant dialogue between ferry companies and the relevant authorities, both in the UK and in France, to ensure the best possible security for passengers.’