Worried Greek anti-terrorist police have used a yacht in a major security exercise to see if an attack on the Olympic Games in a leisure craft could succeed.

Greece is spending £165 million on security measures which include a vessel traffic system which will check all boats – including yachts – entering and leaving Piraeus port in Athens.

There are also fears that the new cruise liner, Queen Mary 2, dubbed the ‘biggest terror target on the high seas’ could be subjected to an attack during her stay in Athens for the Games.