Just as France marks the 10th anniversary of the Bataclan massacres, another reminder has come of the permanence of the jihadist threat.

A former girlfriend of the only jihadist to survive the November 2015 attacks has been arrested on suspicion of plotting her own violent act.

The woman – a 27 year-old French convert to Islam named as Maëva B – began a letter-writing relationship with Salah Abdeslam, 36, who is serving a life sentence in jail near the Belgian border following his conviction in 2022.

When prison guards discovered that Abdeslam had been using a USB key containing jihadist propaganda, they traced its origin to face-to-face meetings that the prisoner had with Maëva B.

Detectives then looked into Maëva B’s own computer and telephone, where they found evidence she may have been planning a jihadist attack, and on Monday she was placed under judicial investigation along with two alleged associates.

With France commemorating 10 years since the worst attack in its modern history, the arrest has focused minds on the enemy that never went away.

Six plots have been thwarted this year, says Interior Minister Laurent Nuñez, and the threat level remains high.

On the evening of 13 November 2015, jihadist gunmen and suicide bombers conducted a sequence of co-ordinated attacks that culminated in a bloody raid on the Bataclan concert hall in eastern Paris.

Before that, three suicide bombers blew themselves up outside the Stade de France where a football international was under way. Then others in the gang opened fire with Kalashnikovs on people drinking in bars and cafés not far from the Bataclan.

There, a performance by American group The Eagles of Death Metal had just started, when three jihadists burst in and fired indiscriminately into the auditorium. They took hostages and then blew themselves up as police moved in.

Overall 130 people were killed, 90 in the Bataclan, and more than 400 treated in hospital. Countless others suffered psychological trauma.

The word Bataclan has since become a byword in France for extreme Islamist attacks, in much the same way that 9/11 did in the US.

Though there have been other attacks since, like the Nice lorry massacre of July 2016 and the beheading of teacher Samuel Paty in October 2020, the scale and organisation of 13 November 2015 set it apart.

Ten years on, much has changed. The disappearance of the Islamic State (IS) group as a major force in Syria and Iraq means that the wherewithal to conceive, plan and carry out complex terrorist projects is greatly diminished.

The Bataclan attackers were young men of mainly North African origin, recruited in Belgium and France, trained in IS territory in the Middle East, who then returned to Europe hidden among a vast flow of migrants.

Everywhere they could draw on a network of supporters offering shelter, transport and cash.

According to leading Middle East expert Gilles Kepel, intelligence services have also become highly effective in controlling online radicalisation.

“They now have access to IT resources… which allow them to detect a lot of individual initiatives, often not very sophisticated ones… and stop them before they hatch,” he said in an interview with Le Figaro.

But according to Mr Kepel, the danger now comes from what he calls “ambient jihadism”.