Kill British Isis fighters, says the defence secretary. It’s not that simple

Defence secretary Gavin Williamson has been widely ridiculed for his hawkish remarks on British jihadists, but both the minister and some of his critics are guilty of oversimplifying a complex legal and political issue to score cheap points. Williamson set out a one-dimensional counter-terrorism policy, with crude body counts at the core. But there are circumstances in which hunting down jihadists across borders is legal, legitimate, and effective – and British passport holders are not exempt.

Williamson made no mention of the law, but this is where we must start. The UK is waging war against Islamic State in Iraq and Syria on two legal grounds. One is that Isis members have planned and directed attacks on the UK, and there is no way to arrest or extradite them. This is the right of individual self-defence. Another is that the UK is coming to Baghdad’s aid on both sides of the border, drawing us into an existing armed conflict. This is collective self-defence.

Isis fighters are not technically combatants, but they lose civilian protections by engaging in hostilities. It is legal and legitimate to kill them, as long as they are not injured or captured. Under international humanitarian law, it certainly doesn’t matter whether an Isis member was born in Cairo or Croydon. In any case, the RAF is not in a position to check the passport of an Isis member driving a bomb-laden truck. Some of the outrage over Williamson’s remarks represents a misplaced squeamishness that substitutes for a proper understanding of the rules governing war. However, in some cases our allies on the ground have captured alleged British Isis members; the defence secretary surely did not intend that the Kurds should execute such detainees, but he might think carefully about the signal he sent.

Even trickier are the Isis members outside Iraq or Syria, such as those who have travelled to Egypt or Afghanistan. Williamson implied he would “hunt them down”. But this is not simply a matter of phoning up the SAS. It would be something of a stretch to claim that a drone strike or raid in the Sinai desert was really about the defence of Iraq. The individual self-defence argument would therefore be required. But pointing out that someone was a member of Isis is insufficient. At the very least, there would have to be evidence that the individual was “actively engaged in planning and directing imminent armed attacks against the UK”, which is one way that the government justified a drone strike on Reyaad Khan in 2015. The use of force would also have to be “necessary” and “proportionate” to the threat.

Williamson’s critics should understand that there are some cases that will meet these criteria. To label them all as “extrajudicial killing” is to commit a basic confusion of domestic laws with the UN Charter. It is polemic rather than argument. But, perhaps disappointingly for the trigger-happy defence secretary, these criteria would apply to only a minority of the several hundred British jihadists abroad who may be spotted beyond Iraq or Syria. Many will be in jurisdictions where the UK has perfectly good relations with the local authorities, such as Turkey or Jordan, nullifying the legal case that force is strictly necessary. If Williamson had spent more time with the attorney general, and less with the Daily Mail, this might have been apparent.

He is on firmer ground in arguing that British jihadists should be excluded from returning to the UK. Last year, 35 terrorism suspects were stripped of their passport, with another 45 in the first half of the year. The European court of human rights backed the UK in one such case in May. But this is not a panacea. For one thing, British-born citizens cannot be left stateless. As long as the UK cares about its obligations under international law, such constraints can’t be waved away. There may also be circumstances in which it is preferable to arrest and prosecute a returning jihadist, rather than have them disappear into the murk of Isis’s worldwide network of provinces and affiliates. As a security source told the Guardian, “our number one preference is to get them on trial”.

Finally, we come to Williamson’s remark that “a dead terrorist can’t cause any harm to Britain”. This is good tabloid fodder, but it misses the point. The international coalition against Isis has killed more than 60,000 fighters in the past three years. Contrary to the views of the Stop the War Coalition and their ilk, this was not bloodlust. It was necessary to halt atrocities against the Yazidi minority, end Isis’s totalitarian rule, and address the terrorist threat at source. But the prospects of victory do not rise in linear proportion to the body count. If watching Ken Burns’s rrecent documentary on Vietnam did not make this clear enough, then there are ample recent examples – not least Isis’s own ascent from the ashes after 2011. As the group loses manpower and territory, it may even splinter in ways that make it more dangerous. No country can kill its way out of the problem.