"Technology plays a huge role in our forces, It often makes the difference between success and failure - and sometimes life and death," said Defence Procurement Minister Lord Drayson on announcing the winners.

"The challenge is to produce a semi-autonomous system that can detect, identify, monitor and report a range of physical threats in an urban environment."

The winner of the competition will win the R J Mitchell Trophy, named after the "father of the Spitfire" WWII fighter plane and also funding from the Ministry of Defence (MoD).

Target lock

In total, the challenge received 23 proposals from firms and research institutions.

Grand Challenge judges have now chosen to fund six of them to compete in the finals; a further eight teams have entered the challenge with private funding.

The competition, carried out in August 2008, will focus on the urban environment and will be carried out at Copehill Down, an army training centre on Salisbury Plain.

Built during the Cold War and modelled on an East German village, the mock-up settlement will be swept by the teams for possible threats.

"There are going to be four categories of targets: an improvised explosive device; a sniper; some kind of four-by-four vehicle with a gun on it; and bunches of 'hoods' dressed in semi-military uniform carrying arms," Mike Martin, chief judge of the challenge, told the BBC News website.

The winner will not necessarily be the team that identifies all of the targets correctly, according to Mr Martin.

For example, a remote-controlled vehicle will lose points for needing input from a human operator.

"Something that is completely autonomous - you just launch it; it goes off, does its own thing and comes back and says unequivocally X, Y and Z are targets - would score maximum points," said Mr Martin.

Urban challenge

The Grand Challenge will deliberately focus on robots that can aid troops in the urban environment, an increasingly common battle arena.

"Urban operations are both very important and they're becoming more difficult to carry out safely," said Lord Drayson. "The challenge of the urban environment is the degree to which you have this unstructured clutter and the unexpected."

Major General John Cooper added: "The threat you are facing is not only small arms, in terms of direct fire, but also potentially anti-tank [weapons]... and increasingly complex improvised explosive devices.

"This is an environment which is growing in density and complexity on a daily basis."

As well as dealing with the sheer complexity of having to differentiate between a sniper and an innocent civilian leaning out of a window, the vehicles will also face a number of environmental hazards.

Of particular concern to the teams, which have been allowed to map the Copehill site, are the wind, trees and the near-invisible overhead cables that criss-cross the site.

"They could be a problem for us because we might be flying quite low, but we should be able to pick them up on the cameras," said Jeremy Old of team Dragonfly.

The privately funded group has proposed a 2m-long, lightweight, hovering vehicle equipped with a zoom lens and with thermal or infrared imaging.

"We can fly quite slowly which will give us time to react, but it all needs thinking about."

Numbers game

The teams now have 12 months to build their prototypes.

Some have relatively simple designs, based around a single vehicle.

Barnard Microsystems, for example, plans to adapt an unmanned aerial vehicle (UAV ) it has designed to survey oil pipelines in remote areas.

Others, such as team Stellar has proposed a multiple vehicle approach. Its Saturn (Sensing and Autonomous Tactical Reconnaissance Network) proposal consists of two different UAVs and an unmanned ground vehicle (UGV).

"The platforms have got autonomous threat detection sensors on them based on visual, thermal and radar," explained Dr Julia Richardson, head of the team.

One of the most innovative designs was proposed by a team from Swarm Systems.

Its proposal consists of eight to 10 "dinner-plate sized" quad-rotor helicopters which would be able to fly in and out of buildings.

"There is only so much information you can capture from one vehicle," Stephen Crampton, the head of the team, told the BBC News website.

Equipped with high-resolution cameras, the swarm will use numbers to its advantage.

"You can get images from different points of view, which is often very important because something you can see from one angle, you can't from another," said Dr Owen Holland, another member of the team.