Watch out: Armed police officers patrol outside the Olympic stadium in the Olympic Park, London

Crosshairs: Royal Artillery Bombardier Johnathan demonstrates a High Velocity multiple surface rot air missile system to local residents at Buxton school in Leytonstone

He told The Mail on Sunday: ‘An Unmanned Aerial Vehicle (UAV) can be put in a backpack. They come in all sorts of sizes and it’s feasible they could be filled with something noxious and flown by remote-control.’

Lieut Col Fahy – the officer responsible for community relations during the Games – made his remarks  on Friday in Leytonstone, East  London, near one of six sites which could see the deployment of surface-toair missile batteries in order to shoot down aircraft attempting to infiltrate an Olympic ‘no fly’ zone.

Fears: An unmanned drone could be used by terrorists to deliver a biological weapon strike, a senior army officer warned

During the meeting at Buxton School, his team showed locals  a ‘dummy’ missile battery and allowed children to play on the unarmed weapon.

Lieut Col Fahy declined to elaborate on what type of poison might be used during an aerial attack.

He said: ‘For the duration of the Olympics anyone flying into controlled airspace is to file their flight plan with the Civil Aviation Authority.

‘The range of threats varies in  size and capability. It could be a commercial airliner hijacked by somebody with malicious intentions or a protest group using a microlight to get their name in the papers.’

His poison warning came as it was revealed that SAS troops have had anthrax emergency training at the Government’s top-secret military research establishment at Porton Down, Wiltshire.

Sources say the elite soldiers wore biochemical protection suits, gloves and masks during exercises over the past few months to prepare for any attack using the deadly bacteria.

Such an incident could threaten the lives of thousands of people attending the Games this summer.

Lieut Col Fahy told The Mail on Sunday: ‘We have worked up a comprehensive plan to protect against the potential hijacking of a commercial airliner down to slow-moving microlights or radio-controlled planes.’

Battle stations: The army placed a surface-to-air missile on top the Fred Wigg tower block in Waltham Forest, est London as part of a series of security tests for the 2012 Olympics

Defence: The surface-to-air missile on top of the Waltham Forest tower block are one of a link of armaments designed to create a ring of steel around the Olympic site

Repurposed: The Fred Wigg Tower in Waltham Forest, London, has been chosen as one of six sites around London to form a 'ring of steel' to safeguard the Olympic Games

Practice: Setting up ahead in Blackheath, of a training exercise designed to test military procedures prior to the Olympic period

Training time: A member of the Royal Artillery aims the Starstreak High Velocity Missile System, part of the ground based air defence systems that may be deployed during the Olympics, at Blackheath, London

Lieut Col Fahy also revealed that armed police would guard any  missile sites being used in case any attempts were made to steal them or protest against their deployment.

He added: ‘What we are doing is unusual. Londoners are not used to seeing a lot of soldiers around. Some people feel uncomfortable about the missiles but the vast majority, I think, appreciate we are doing this.’

HMS Ocean, one of the UK’s biggest warships, is based in the Thames, with the capability to fire a hail of missiles at a terrorist aircraft.

The awesome array of military hardware ready to thwart an attack includes four RAF Typhoon jets, three Royal Navy Sea King and two RAF Puma helicopters.

A Ministry of Defence spokesman said last night: ‘We are prepared for any eventuality.’