Video: London 2012 Olympics: missile defences 'designed to reassure' "The exercise is designed to reassure the public and the Olympic movement that security is taken seriously," said Mr Clarke, director of the British security thinktank, the Royal United Services Institute. It is also to create a deterrent to anyone that is going to have a go, that if they do they will probably die. After recent criticism of MoD plans to install missiles on the roofs of residential properties in east London, Mr Clarke stressed that Olympic security plans would not see the heavily armed British forces roaming the streets. He said: "After this exercise, you won't be aware of the military at all, the Olympics will be entirely police led, unless something goes terribly wrong." The defence expert also addressed public concerns about the potential dangers of using missiles in skies over such a built-up area. If anything is intercepted by missile ... it will break up, bits will fly around no question. That is relatively dangerous but the calculation is that is a lot less dangerous than letting something get through.