The RAF is planning to use Reaper robot drones for surveillance and intelligence-gathering during the 2012 London Olympics as part of the largest security operation ever mounted in the UK.

It will be the first time that unmanned aircraft have been allowed to fly over the crowded capital, although it is likely they will be operating within an air exclusion zone in force for the period of the games to minimise the risk of accidental midair collision.

Manned fighter aircraft will be stationed at several bases within easy flying distance of London to meet the threat of a hijacked airliner being used in a 9/11-style terrorist suicide attack while the Reapers will be used to track movement on the ground.

The drones, remotely controlled by pilots, are fitted with a range of infra-red sensors, ground-scanning radars, electronic eavesdropping equipment and high-definition cameras which allow them what RAF sources describe as "a God's-eye view of the battlefield".

The RAF has three Reapers and used at least one for surveillance in Afghanistan to relieve pressure on Britain's ageing and fuel-leak-prone Nimrod MR2 spy jets.

The drones are second- generation models of the Predator unmanned aerial vehicles which made their combat debut under CIA control during the US-led invasion which toppled the Taliban in 2001.

They have since been used extensively in Iraq and Afghan-istan to launch strikes against high-priority insurgent targets and al Qaeda leaders with US Hellfire guided missiles.

The RAF's top brass have now submitted a £500m urgent operational requirement bid to persuade the Treasury to buy 10 of the aircraft to equip a full operational squadron.

The three already acquired are being flown from Kandahar airbase by teams from 39 Squadron, a unit formed last March which contains RAF, Army Air Corps and Royal Navy aircrews.

Each Reaper mission can last as long as 14 hours and needs two complete crews to allow for rest periods for those manning the consoles. By contrast, the average manned fighter-bomber sortie lasts five hours or less.

While US drones have strike missions as their main function, the RAF foresees that surveillance and intelligence-gathering will be its priority.