Boffins at Britain's Ministry of Defence have invented an electric 'force field' designed to protect armoured vehicles against anti-tank grenades.

The 'electrical armour' is designed to vaporise copper projectiles released from grenades on impact before they are able to penetrate a tank's inner hull, the Daily Telegraph reports. The idea is to make tanks less vulnerable to anti-tank launchers, such the RPG-7, which is commonly and cheaply available in the world's trouble spots, such as Afghanistan.

When armaments like RPG-7 grenades hit a tank, a "shaped-charge" warhead blasts a jet of hot copper into a target at around 1,000mph - capable of slicing through a foot of conventional solid steel armour.

The new electric armour is based on a highly charged capacitor connected to two separate metal plates on the tank's exterior. The outer (armour-plated) plate is earthed while the insulated inner plate is live.

When the crew of a tank feel they are under danger, they switch on current to the inner plate, using the tank's internal power supply.

If the tank is unfortunate enough to be hit by a grenade, the jet of copper produced will penetrate both the outer plate and the insulation of the inner plate completing a circuit, which results in the discharge of the capacitor and the vaporisation of most of the copper.

The Telegraph reports that despite the high charge generated by the system, the "electrical load on the battery is no more than that caused by starting the engine on a cold morning".

It sounds bizarre, but the paper reports that in a recent demonstration an armoured personnel carrier protected by the system withstood repeated attacks by rocket grenades that would normally have destroyed it many times over.

Boffins hope to develop the armour further and fit it in Britain's next generation of tanks and armoured personnel carrier. The Pentagon is also reportedly showing a keen interest in work on the technology. ®