New air restrictions over London have come into force which could see aircraft deemed a terrorist threat dealt wit using “lethal force” as a last resort.

RAF Typhoon jets and RAF Puma helicopters with snipers armed with hi-tech rifles will be among the military aircraft patrolling the restricted zone.

Intercepted aircraft will be expected to comply with the directions of the military aircraft.

“As a last resort, we will have lethal force as an option,” said Air Vice-Marshal Stuart Atha, the Olympics air security commander.

Asked who would give the order for lethal force to be used, AVM Atha said: “The highest level of government makes that decision.”

He said taking lethal action would be a “worst-case scenario” and that a best-case scenario would be to intercept and gain knowledge of the seriousness of the situation away from the built-up area of London.

The restricted zone, in operation to August 15, comprises a small inner zone covering central London and the Olympic site in Stratford, east London, and a large zone covering a swathe of south-east England.

The restricted zones are designed for general aviation which includes light aircraft, gliders and balloons. No commercial flights will be affected.

A Home Office spokesman said that for the Olympics “we are planning on a terrorist threat environment that is severe”.

But he went on: “We are not suggesting that there is any particular threat or risk to the Games that we know about.”

Under the plan, general aviation will not be allowed in the inner zone, although passenger planes heading for Heathrow and London City Airports will not be affected.

Private pilots wanting to fly in the larger restricted zone will have to file a flight plan and comply with Ministry of Defence instructions.

Aircraft intercepted will have to rock their wings, follow the military aircraft and turn away from London.

Flares and lasers could be fired by the military aircraft, then, as a last resort, if an aircraft fails to comply with the directions of the military aircraft, it may be considered to be a threat to security, which may result in the use of lethal force.

Defence Secretary Philip Hammond said: “Whilst there is no reported threat to the London Olympics, the public expects that we put in place a range of measures aimed at ensuring the safety and security of this once-in-a-generation event.

“I am pleased to be able to confirm that the equipment necessary to operate our comprehensive, layered air security plan is now in place.

“I believe this will provide reassurance to residents of, and visitors to, London, and a powerful deterrent.”