LONDON, Jan 7: British anti-terrorist police said on Tuesday they had found a small quantity of ricin, one of the world’s deadliest toxins, in London raids that led to the arrest of seven north Africans.

Ricin — which terrorism experts linked to al Qaeda — was notoriously used to assassinate Bulgarian exile Georgi Markov in London in 1978 with a poison-tipped umbrella.

There is no known antidote to the poison, which experts say is easy to make and stockpile. A small dose can be lethal and causes flu-like symptoms for a few days before death.

“This is all about the psychology of fear, planting terror in people’s minds,” Magnus Ranstorp, a terrorism expert at Scotland’s St Andrews University, told Reuters.

Ranstorp said he had seen instructions on how to create ricin in literature from al Qaeda, blamed for the September 11 attacks on New York and Washington.

Police would not make any link to al Qaeda, saying only that they had arrested six north African men and a woman, who was later released, under the Terrorism Act.

The arrests were made during raids in north London on Sunday, the latest in a line of clampdowns in Britain.

The British government has issued a series of warnings in recent months, saying Britons are in “the front line” because of London’s strong support for the U.S.-led war on terror.

Prime Minister Tony Blair, who recently said he was bombarded almost daily with tipoffs about possible attacks, said on Tuesday it was “only a matter of time” before terrorists got hold of weapons of mass destruction.

“As the arrests that were made earlier today show, this danger is present and real and with us now, and its potential is huge,” he said as Britain mobilised for possible war against Iraq.

Police urged the public to remain vigilant.

“We have previously said that London and indeed the rest of the UK continues to face a range of terrorist threats from a number of different groups,” said David Veness, head of Britain’s anti-terrorism police.

“Our message is still alert not alarm.”

The Times newspaper said in November 2001 that al Qaeda was planning to manufacture ricin after instructions for making the poison were found in an abandoned house in Afghanistan that it said had been used by Osama bin Laden’s network.

The instructions read: “A certain amount, equal to a strong dose, will be able to kill an adult and a dose equal to seven seeds will kill a child. Gloves and face masks are essential for the preparation of ricin. Period of death varies from 3-5 days minimum, 4-14 days maximum.”

The government said it had alerted health officials in case members of the public had been affected.—Reuters