RN ships should be equipped with pump guns that can draw pig blood from a tank and spray it on the surface of the water. When the invaders jump out of the boat, spray the area and leave. The sharks will smell the blood very quickly.
Don’t know if there are sharks in the Channel, but spray pig blood and you will see muzzies dancing on their tippytoes on the surface like flyingfishes to avoid contamination by pig.
Brits have the Royal Navy. Yanks have the Second Amendment.