A leading expert on Algerian extremists has blamed the 11 September attacks in New York and Washington on the West's failure to heed the warnings of the 1995 nail bomb attack on the Paris Metro.
There were several attacks in France in the 1980s and 1990s
Eight people were killed and scores of others injured in the bombing, which was linked to the Armed Islamic Group, or GIA.
It followed a spate of explosions in Paris in the 1980s and 1990s, and a foiled Algerian suicide plot to fly a plane into the Eiffel Tower.
Former chief prosecutor in the French anti-terrorist courts, Ms Irene Stoller, told the BBC's File on 4 radio programme that for too long the authorities in London refused to act because they did not feel directly threatened.
"It was a case of 'It's happening to my neighbour, not to me, so it's not my problem,'" she said.
"It has allowed all these networks to install themselves, to grow, to learn to fight and to carry out a number of attacks across the world.
"If all Europe had fought against the problem from 1995, as we did, we would not have had the 11 September [attacks]."
Since the 1995 attack, France's anti-terrorist directorate has joined its intelligence, police and judiciary to work under joint command.
They have made sweeping arrests, in one celebrated case putting more than 100 people on trial at once.
I know the names of people who were killers in Algeria. I have told the immigration service about them, but the authorities told me it was nothing to do with me
Algerian Refugee Council's Dr Mohammed Sekkoum
But Ms Stoller said the lack of political will amongst Americans and Europeans meant terror cells spread from bases in French cities such as Lyon, Paris and Marseilles, through much of Europe.
"It's difficult to say how many there are - several thousand passed through the training camps," she said.
"The intelligence services say that across Europe there are several hundred people who are ready for war and determined, the day they receive their order, to attack."
Police intelligence in Lyon has tracked al-Qaeda's "false imams"; those who recruit frustrated and alienated young men from run-down estates and transform them into active ┐terrorists".
A senior officer, who did not want to be named, told File On 4:
"There are up to five dangerous imams in Lyon. Many young people in the estates have disappeared for a while.
"We know that they leave France, go to London where they are given new passports and identities, and then go to the training camps where they learn to plant bombs."
Back in the UK, the Algerian Refugee Council chairman, Dr Mohammed Sekkoum, says a substantial number of active "terrorists" have slipped into the country with their families, seeking asylum.
Campaigners argue that Britain should resist further French-style clampdowns
"If you're in the Algerian community, you know these things," he said.
"Most of the people who come here are law-abiding people who came with nothing and have strived to work hard.
"But I know the names of people who were killers in Algeria. I have told the immigration service about them, but the authorities told me it was nothing to do with me."
A running sore in Anglo-French relations is the UK's refusal to extradite an Algerian accused in connection with the 1995 attack in the Paris Metro.
In the months after the bombing, Rachid Ramda was arrested in London.
Human rights 'violations'
The French wanted to put him on trial but when the UK Home Secretary David Blunkett finally gave the order for his extradition it was blocked in the High Court.
The judges were worried that some of the evidence against him had been beaten out of one of the bombers by the notoriously tough French anti-terrorist police.
Campaigners here argue that Britain should resist any further French-style crackdowns and say they are worried at the government's decision to opt out of part of the European Convention on Human Rights.
Listen to this week's File On 4 on BBC Radio 4 at 1700 GMT on Sunday 7 March