In the occupied Palestinian territories, you can tell who the 'engineers' are: they are the ones covered in burn marks who might be missing fingers, or even a whole hand.

The engineers are the bomb-makers for the young suicide bombers sent to kill Israelis by the Islamic militant organisations such as Hamas. And their explosive of choice, triacetone triperoxide or TATP - named today as an explosive used in last week's London bombings - is the reason for their disfigurement.

TATP's base ingredients - drain cleaner, bleach and acetone - can be bought easily and without attracting suspicion; its chemical composition is simple; and in its finished form it is almost undetectable by sniffer dogs or conventional bomb detection systems.

For the same reasons that Hamas uses TATP to send suicide bombers undetected into Israel, the al-Qaeda network has adopted TATP for its terror missions abroad. The substance was included as the trigger in the shoe bomb that Briton Richard Reid tried to detonate on a flight from Paris to Miami in December 2001, and in the identical device given to Reid's fellow bomber Sajid Badat, who aborted his mission.

But as the Palestinian bomb-makers will attest - 40 Palestinians are thought to have been killed making or handling the explosive - it is highly unstable and sensitive to heat and friction. Not for nothing is it known as "Mother of Satan".

As one British explosives expert said today of the news that TATP was involved in the four London blasts: "Frankly, I wouldn't like to be wandering around with 10lb of TATP on my back."

That expert suggested that TATP - which does not need sophisticated detonating devices - might have been used only as the trigger for the London bombs, but it could have been the main explosive. "It would be surprising, but then the Jihadis, and al-Qaeda, are always capable of surprising us," he added.

In Reid's case, there was a small thread of TATP running through 100 grammes of PETN, a high-grade military plastic explosive, attached to a powder-fuse running through his shoelace. That combination surprised bomb experts - TATP is not the trigger normally used for PETN - but was seen as a sophisticated mixture for avoiding detection.

Although discovered as far back as 1895 by a German scientist, Richard Wolffenstein, TATP's instability meant it was never taken up militarily or commercially. But it was rediscovered in the West Bank in the early 1980s and soon became an extremists' staple.

Instructions for making TATP can be found relatively quickly on the internet. Anthony Loyd, a Times reporter, found similar instructions in documents abandoned in an al-Qaeda safe house after the fall of Kabul in November 2001.

TATP is thought to have been used in used in various bomb attacks outside the Middle East, including on a Philippines Airlines flight to Japan in December 1994. It was also used as the trigger in two car bombs detonated in London in July 1994 outside the Israeli Embassy and a Jewish philanthropic institution. Two Palestinian students were later convicted of conspiracy over those bombings.

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