As a rule of thumb, the French media reported massacres in Algeria’s long-running civil war if the dead numbered more than 20; in Britain, the death toll had to reach triple figures or involve a spectacular atrocity by the Islamic guerrillas, such as the annihilation of an entire village, before it was reported. In France, the apparently endless cycle of violence in its former colony received limited coverage. In Britain it had little or none.

Few foreign journalists got into Algeria; those that did found reporting frustrating and dangerous as well as unrewarding. There was little appetite for news about this ugly, complicated, far-off conflict. And so the war festered on, and still does: only 11 days ago 49 Algerian soldiers were killed in an ambush.

That event might merely have been added to the long litany of bloodshed and then forgotten, had it not been followed by the arrest in Britain of a group of suspected Algerian terrorists allegedly manufacturing the poison ricin. The vicious but distant civil war that has raged on the edge of Europe for more than a decade suddenly seemed very close.

The horror started in 1992, when the Algerian Army intervened to overturn elections the Islamic fundamentalists were poised to win, sparking a brutal war between radical religious groups and the secular, military-backed Government. Neither side had a monopoly on atrocity. The victims, mostly civilians, are thought to number between 100,000 and 150,000 dead. It is a mark of a forgotten war when such a margin of “give or take” can be 50,000 lives.

The Algerian conflict was an ideal seedbed for Islamic terrorism. Like Afghanistan, the country was left to its civil war; as in Afghanistan, the result was an ultra-violent perversion of Islam, reinforced by poverty, international isolation and a culture of endemic violence. As with Afghanistan, the Algerian carnage was widely ignored by the West — until it arrived there.

The Algerian Army claimed to have killed 15,000 Islamists, but terror thrived: young zealots from Algeria trained in Afghanistan and alongside Chechen militants in Georgia. The radicals moved from slaughtering Algerian peasants to attacking foreign targets, first within Algeria, then in France, most dramatically with the bombing campaign on the Paris Métro that erupted in 1995. The hardline Armed Islamic Group, or GIA, fractured into smaller groups, notably the Salafist Group for Preaching and Combat, believed to be linked to al-Qaeda.

France launched a crackdown, and President Bouteflika of Algeria offered an amnesty; some armed militants gave up the fight, but others took it with them, to Afghanistan, to Chechnya and, inevitably, to Britain.

When the French authorities cautioned that Britain was becoming a magnet for a terror diaspora, the response was more a shrug than a shudder. But the arrests in London and Manchester, and the murder of a policeman, have finally woken Britain to the Algerian terror laboratory that has been churning out militants for a decade.

The contrast between the two countries is stark. In France, under direct attack, the inquisitorial judicial system went after the terrorists, but we preferred merely to “monitor” suspected militants. European diplomats grimly referred to “Londonistan”, pointing to our liberal asylum laws and tolerance of extremist propaganda in British mosques. As many as 40,000 Algerians may have arrived here over the past decade, but officials rechecking asylum applications say they have so far been able to trace only a fraction.

French fury at what they see as lunatic leniency on Britain’s part has focused on the case of Rashid Ramda, an Algerian granted asylum in Britain in 1992 and accused by France of masterminding the bombing campaign on the Métro. For nearly eight years the Home Office has refused to extradite Ramda; only after 9/11 did David Blunkett finally sign the extradition, which was then overturned by the High Court pending an evaluation of whether the suspect’s safety could be assured if he was handed over to France.

The French, signatories to the same human rights conventions as Britain, are understandably livid, seeing the Ramda case as symptomatic of a failure to appreciate and act on the Algerian threat. Frustrated by Britain’s policy of “watchful tolerance”, French secret service agents are now said to be conducting their own surveillance of the Algerian community in Britain.

The Government points out that the new Anti-terrorism, Crime and Security Act gives unprecedented powers to detain anyone whose presence is deemed “not to be conducive to the public good”, and next month two Algerians will stand trial charged with membership of al-Qaeda. If convicted, they will be the first people to be sentenced in Britain on charges related to international terrorism since 9/11.

Britain responded to last week’s events and the murder of a Manchester detective as if the Algerian connection was somehow a new phenomenon, rather than a well-established menace. The danger now is that after years of public or political indifference, the sudden and dramatic focus on Algerian terrorism may provoke a backlash against the thousands of genuine Algerian asylum-seekers who have found sanctuary from a horrific conflict.

Britain’s error has been to view the Algerian civil war as primarily an internal or a French problem, in rather the same way that European governments have regarded the conflict in Northern Ireland as a localised British matter. Many Britons, until last week, were unaware of the continuing civil war in Algeria, let alone of its relevance to Britain.

As Britain tries to tread the line between national security and preserving civil liberties, the failure to assess the Algerian threat adequately is a stark reminder that in the 21st century there is no such thing as someone else’s war.

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