Reports from France suggest that heavily armed troops and police have been sent to ports, including Calais, to defend against an Islamic State (Isis) attack on a UK-bound ferry. Security services both sides of the channel are on high alert to counter any Isis (Daesh) planned atrocity on a crowded vessel between Great Britain and France.

As the extremists lose ground in their self-declared caliphate that bridges Syria and Iraq, cells of terrorists allied to the group are increasing attacks in the West. In the last week, 86-year-old French priest Father Jacques Hamel, 86, was murdered in a Normandy Church, whilst Germany was rocked after an IS suicide bomber attacked a music festival in Ansbach, injuring 12 people and killing himself.

Passengers between the ports either side of the Channel are being heavily vetted by security staff. This weekend travellers heading to France from Dover are facing heightened security checks by French officials in the wake of the terror attacks with large queues expected.

A senior UK security source said to the Mirror: "The presence of the police and soldiers near Calais is very alarming – there's nothing routine about it. Apparently, they are at a high state of alert because there is a fear of jihadists getting on to a ferry headed for Britain and executing people on the ship.

"It is also possible that Isis may have been told security has in the past been reasonably lax so they believe they can get terrorists into Britain via a ferry."

British Special Forces commandos, including the Royal Navy's equivalent of the Special Air Service (SAS), the Special Boat Service (SBS) – are trained in resolving violent crisis situations on vessels in at sea,

A counter-terror source said: "What we've learned from the attacks across Europe is that prevention is paramount. Once an attack is underway, the terrorists have already got what they wanted."

French security services have come under fire recently after it emerged that attacker that slit the throat of Hamel, Adel Kermiche, had tried to get to Syria twice in 2015 and was wearing an electronic tag that was switched off for four hours every morning.

President Francois Hollande has said France is planning to form a National Guard to prevent future atrocities and flood transport hubs and crowded areas with armed security.

P&O ferry
Security services are planning for an Isis attack on UK-bound ferry Getty