The terrorists' weapon of choice: Arm it, fire it, run

The rocket-propelled grenade that was used to blast the MI6 building is a handy terrorist weapon - it is easy to use and easy to conceal.

The rocket-propelled grenade that was used to blast the MI6 building is a handy terrorist weapon - it is easy to use and easy to conceal.

But although the Soviet-made RPG7 anti-tank device has been a popular weapon of terror in Ireland, Wednesday night's attack is believed to be the first time it has been deployed on the British mainland.

The weapon was identified after parts of the launcher were found by police close to the MI6 headquarters last night.

Designed to penetrate armoured steel on a tank, the RPG7 has little impact on buildings and in some cases in Northern Ireland has passed right through the walls with little damage.

But by hitting the prestigious MI6 headquarters in the centre of London it has made a huge impact with the world's press and sent a warning shot to the Government and security authorities.

Paul Beaver, a spokesman for the defence publication Jane's, said that the weapon used in the assault was probably a variant of the RPG7.

He said the weapon weighs 7.5kg and can fold in half to easily fit under a coat or into the boot of a car. It is now mainly used in developing countries and would be targeted against lightly armoured vehicles.

The grenade is normally fitted with an armour-piercing head but the limited damage done to the Vauxhall building suggests it was either adapted to contain an explosive or malfunctioned.

"It is not a very effective weapon," Mr Beaver said. "It takes less than 25 seconds to go through the motion of arming it, then you fire it and run."

Another disadvantage of the weapon is that it has been known to malfunction, with the rocket propellant working but the grenade failing to explode.

When fired, the weapon produces a double explosion: the first when the grenade is launched and a second moments later when it hits the target. According to eyewitnesses, the second blast was sufficient for them to feel it underground.

Mike Yardley, a terrorism expert, said: "We know that it [the RPG7] is a weapon that has been in possession of, for example, both the IRA and Middle Eastern terrorist groups."

The break-away group believed to be behind Wednesday night's attack, the Real IRA, has access to a considerable arsenal of weapons and explosives - including rocket launchers - which they seized from secret arms bunkers before splitting with the mainstream republican leadership.

In July, a huge shipment of arms and explosives bound for a group of breakaway republican terrorists was seized by Croatian police in the port of Split.