The ingredients of the July 21 bombs were acquired in the high street and required little more than a rudimentary knowledge of chemistry to make up. The shopping list of the alleged bombers included hydrogen peroxide — widely used in hairdressing — chapati flour, nail polish remover (acetone), sulphuric acid, batteries, torch bulbs, electrical wires, cardboard and half a dozen food storage tubs, Woolwich Crown Court was told yesterday.

The components were taken to the flat of Yasin Omar for assembly into improvised explosive devices.

That one-bedroom council flat, on the ninth floor of Curtis House, a tower block in New Southgate, North London, was described at the court as the alleged terror cell’s “bomb factory”.

There, three members of the gang are said to have spent long hours sweating over the electric cooker in the small kitchen, boiling huge panfuls of liquid hydrogen peroxide to reduce the chemical into a stronger concentration.

Mr Omar, who has studied for a GNVQ in elementary science at Enfield College, Muktar Said-Ibrahim and Manfo Kwaku Asiedo were said to have worked in shifts from 5am until 11pm each day.

Two large saucepans and a frying pan that were recovered from the building revealed, after scientific examination, clear traces of concentrated hydrogen peroxide.

The liquid peroxide was the most important ingredient. Increasingly it is used in the hairdressing trade as a cream but the gang was said to have identified outlets in Finchley, Tottenham and Finsbury Park where they could buy it as liquid in an 18 per cent concentration. Between the end of April and July 5, 2005, they are alleged to have bought 443 litres in either one-litre or four-litre containers.

The peroxide was to form the bulk of what Nigel Sweeney, QC, for the prosecution, described as the main charge of the bombs.

Mr Sweeney said: “The explosive was intended to consist of liquid hydrogen peroxide, concentrated, mixed with chapati flour, the flour being the fuel that would burn and the hydrogen peroxide providing oxygen, so that when fired by a detonator the mixture would explode.”

This concoction was placed inside a series of 6.25-litre plastic kitchen storage tubs that were sealed with a lid. A hole was cut in the bottom of the container, into which a detonator was inserted.

The detonator was made from a small carboard tube packed with the homemade explosive triacetone triperoxide, better known as TATP.

This was, in turn, to be set off with a small torch bulb attached to one end of the TATP tube and linked by wires to a 9-volt battery, the court was told.

The bulk of the bomb was to be hidden in a rucksack and it could be detonated without suspicious activity.

Holding up a replica of the device in the courtroom, Mr Sweeney showed that screws, washers, nuts and bolts had been taped to the outside of the plastic tubs to cause further injury to passengers.

He said: “The purpose of shrapnel is, of course, to increase fragmentation when the bomb explodes and thus to maximise the possibility of injury, fatal or otherwise, to those in the vicinity.”

Extensive tests were carried out by the Forensic Explosives Laboratory using the bomb recipe that was allegedly deployed on July 21 and a variety of detonators. In all cases the devices proved to be “functional”.

The jury was shown slowmotion films of TATP detonators exploding and a full-sized replica device being set off in a quarry. The power and force of the explosions filled the screen and, in the case of the full-sized bomb, a shock wave was clearly visible emitting from the centre of the blast.

On July 21, it was alleged, something had gone wrong with the mixture of the main charge in all four bombs that the gang tried to detonate. Another bomb was abandoned.

Mr Sweeney said that the failure of the bombs to detonate “owed nothing to the intentions of the defendants”.

The trial continues.

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