LORRY bombs loaded with home-made explosive have become the chosen weapon of mass destruction for terrorists from al-Qaeda to the Provisional IRA and far-right American extremists.

The half ton of ammonium nitrate uncovered yesterday in a storage centre in West London could have been converted with fuel oil and a detonation charge into a device capable of killing hundreds.

Bombs of a similar size detonated by the Provisional IRA destroyed the Arndale Centre in Manchester at a cost of nearly £1 billion, and killed two men in South Quay, East London, in 1996, creating damage costing £170 million.

Yet ammonium nitrate, used routinely for military explosive manufacture, can be found in the potting shed of every gardener as an ingredient of general fertilisers.

Farmers use it as a main source of nitrogen to improve their land. The chemical is usually sold in half-tonne consignments and the haul found in Hanwell yesterday would have cost only about £65, according to dealers.

But ammonium nitrate is also used in the manufacture of explosives and is a cheap and readily available bomb-making ingredient.

Mike Yardley, a former army officer and security expert, said: “Terrorists and militants use the ammonium nitrate because it’s incredibly stable to store. The risk of terrorists injuring themselves whilst handling ammonium nitrate is dramatically reduced compared to other explosives.”

Garth Whitty, a former weapons inspector and now head of the Homeland Security department of the Royal United Services Institute, said that ammonium nitrate was not effective in isolation. “But it’s very easy to make a bomb with it, provided you know what you’re doing,” he said.

Last year al-Qaeda and its allies used ammonium nitrate in attacks on three compounds housing foreigners in Riyadh, Saudi Arabia, killing 29.

It was also used for the suicide bomb attacks on the British Consulate and a bank in Istanbul which killed 160, including the British Consul.

But most countries, including the US and Australia, do not regulate the sale of fertiliser-grade ammonium nitrate. In the EU fertiliser-grade ammonium nitrate is manufactured to higher standards than the explosive grade with large, dense granules to prevent them absorbing fuel oil. Stabilisers are sometimes added to prevent the granules breaking down, and fertilisers may be marked so any bomb can be traced to its source.

In Britain suppliers are supposed to inform the authorities of any irregular or sudden inquiries about buying large amounts. But police say that the system is nowhere near tight enough and are planning to lobby for more controls.

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