France's top anti-terrorism judge, Jean-Louis Bruguiere, has warned that al-Qaeda is now more fragmented and a bigger threat than before.
Judge Bruguiere: Al-Qaeda is "bigger, more scattered, more difficult"
He told BBC Radio 4's Today programme that al-Qaeda had attracted younger recruits radicalised by the Iraq war.
"We have a multiplication of all the cells, groups and connections," he said, warning that "unknown elements" were being recruited very quickly.
Judge Bruguiere stressed the importance of identity cards to prevent terrorism.
He also said the courts should be allowed to consider evidence gathered by wire-tapping - as in France, but unlike the UK, where it is inadmissible.
On the al-Qaeda threat, he said "the difficulty that we have is especially with the problem of Iraq... the situation is more confused, more complicated than before".
He said compulsory ID cards had proved "very important" in his country's effort to thwart attacks.
"We have a lot of legal means you (the UK) don't have and these legal means allow us to control and possibly prevent terrorist activities.
"You have the capacity right now, despite the fact there are tough immigration controls, to go from France or continental Europe to the UK with false papers.
"And if you don't have this possibility, to have a database, to know exactly and to control individuals which would be suspected to use false papers in terrorist activities, you miss things."
In the 1990s, Mr Bruguiere focused on the activities of Arab veterans of the 1980s war against Soviet troops in Afghanistan, especially Algerian militants who carried out several attacks in France.
He became an expert on the various cells of Islamist militants operating around the world, many of them loosely linked to Osama Bin Laden's al-Qaeda organisation.