With the brouhaha that happened with the failure of G4S to provide enough security personnel for the London 2012 Olympics, leading to the British Government to call in soldiers from British Military, the latter have been in the planning all along, with special units working behind the scenes and out of sight and fully armed. Whilst you can see the Metropolitan Police Armed Response Units (ARU) fully visible as they make patrols at Olympic venues, the long range ones are somewhere where snipers can have a good tactical view.