The widely-cited statistics of terrorist suspects in the UK are headline-grabbing but are not quite as alarming as they might appear. The 20,000 ‘closed subjects of interest’ to MI5 are closed cases which pose a residual risk: they have appeared on the security radar, but there is nothing to suggest they are actively involved.4
From the Government’s perspective, these individuals pose a political or reputational risk, as much as a security one. However, as the UK’s senior counter-terrorism police officer ACSO Neil Basu has pointed out, it is more important to focus on the 3,000 active subjects of interest.5
These are individuals believed to be linked to terrorist investigations, and therefore they pose a higher risk. But this figure is also, in part, a measure of police and MI5 capacity: in 2004-5, when AQ was planning major attacks against the UK and the US, the number of international terrorist suspects was much lower, at 500-800.6
And police and intelligence service successes mean that Islamist terrorists are less strategically ambitious, and so more inclined to use weapons at hand, such as knives and cars. We should expect this to remain the case.