One of six men on trial for plotting suicide attacks in London in 2005 bought unusually large amounts of hydrogen peroxide in the months before the alleged bomb attempts, witnesses said on Thursday.

The chemical, used for bleaching hair, was a principal component of the bombs which four of the defendants attempted to explode on underground trains and a bus on July 21, 2005, according to the prosecution.

A defence lawyer for Manfo Kwaku Asiedu, one of the defendants, accepted that he was the man described by the witnesses as making the purchases at Sally's and Hairways, two London stores supplying hair and beauty products.

A Hairways employee, Stacey Luck, said the man had asked for hydrogen peroxide at around 70 percent concentration - some four times higher than the highest strength on sale, which was 18 percent.

"It was a very unusual thing to ask for, but he did insist that he had purchased it before," she told Woolwich Crown Court.

When told it was not available, he then asked to buy "something like 48 gallons" of the 18 percent product, she added, and said that he would be placing regular orders.

Sandra Sealey, a former store manager at Sally's, said she first remembered seeing the man on May 9, 2005 when he bought 14 litres of hydrogen peroxide - all that was in the store.

He bought a further 204 litres for cash - all at the highest 18 percent concentration -- on four subsequent visits, culminating with a purchase of 120 litres on June 30.

"He said it was for stripping paint," she told the court. She and a colleague, Orlando Baghaloo, had been surprised by the purchases. "We just kind of questioned it between us."

Baghaloo, also appearing as a witness, said the store would normally sell only three or four bottles a month of hydrogen peroxide at that strength.

The prosecution has alleged that the defendants constructed bombs at a North London flat using flour and hydrogen peroxide. It says they bought hundreds of litres of the chemical and boiled it down to increase its concentration.

The six - Asiedu, Yassin Hassin Omar, Ramzi Mohammed, Muktah Said Ibrahim, , Hussein Osman and Adel Yahya - are all men of African origin in their twenties. They deny the charge of conspiracy to murder.

The prosecution says they were engaged in an "extremist Muslim plot" to bomb London in July 2005, exactly two weeks after four young British Islamists killed 52 people in suicide attacks on underground trains and a bus.

Prosecutors say the alleged plot was not a hastily assembled "copycat" attempt to replicate the carnage of the first attacks on July 7 -- as many people suspected at the time -- but a conspiracy dating back at least several months.