News in early February that Alexanda Kotey and El Shafee Elsheikh, the two remaining alleged members of the so-called “Beatles” gang of British Islamic State (IS) jihadis, had been captured in Syria reportedly created a diplomatic dispute between the US and Britain. Neither country wanted to assume responsibility for their prosecution.

It’s estimated that some 850 British citizens have travelled to fight in Syria and Iraq since the conflict there erupted in 2011. By early 2018, almost half of them had already returned. But what should be done with British fighters who wish to return to the UK after participating in the Syrian conflict?

Hardliners such as Britain’s defence secretary, Gavin Williamson, believe that Britons who fought for Islamic State abroad should be hunted down and killed to ensure they never return to the UK. His US counterpart, secretary of defense James Mattis, expressed similar views. In a special debate on returning British jihadis at the House of Commons in January, Conservative MP Bob Seely pointed out that it’s easier to kill a British jihadi in Syria than it is to arrest, turn or rehabilitate them.

It seems that, for a while at least, the US-led coalition against IS took this hardline approach. For example, the notorious executioner Mohammad Emwazi, also known as “Jihadi John”, was killed by a drone strike in November 2015. The British government estimates that 15% of those who had travelled to Syria and Iraq were killed during the conflict. But with the collapse of IS strongholds, the window of opportunity to use drones and other means to target Western militants who had joined the organisation is closing fast.

Because Britain is a signatory of the 1961 UN Convention on the Reduction of Statelessness, the Home Office can only deprive a person of their British citizenship if they have dual citizenship. Such cases are rare.

Some historical lessons can be drawn from the way Britain and the US handled the return of their citizens who fought as part of the International Brigades in the Spanish Civil War in the late 1930s. In both countries, the government was deeply suspicious of the ideology that took these men and women to Spain.

Most of them were communists, members of a party that was perceived as being bent on revolution and overthrowing the governments in Britain and the US. Yet the British security services were sensible enough to understand that these volunteers were not a monolithic group. Some were not ardent ideologues, others had become disillusioned during the war in Spain. As a result, many veterans of the International Brigades were able to enlist in Britain’s armed services and take part in World War II.

In the US, the Office of Strategic Services enlisted veterans of the International Brigades to help train new recruits in guerrilla warfare. Part of the rationale behind the incorporation of these “reds” into the war effort was that it would be easier to keep an eye on them in the military than it would in civilian life.

There are, of course, clear differences between the situation in Europe in 1939 and today. The risk that today’s returning fighters pose is very tangible. At least five of the men who carried out the attacks in the Bataclan theatre and elsewhere in Paris in November 2015 had been to Syria and joined the ranks of IS before returning to Europe. However, so far, those Britons who have returned from the conflict in Syria and Iraq have not been involved in terror attacks. Those men were radicalised in other ways. Not all foreign fighters become domestic terrorists and not all terrorists start off as foreign fighters.

Perhaps for that reason, not everyone in the security services or the government is convinced that those who return pose an immediate threat. MI5 director Andrew Parker said that those who have come back from Syria are subject to risk assessment. A minority were prosecuted in accordance with counter-terrorism legislation, but most weren’t and are, presumably, being monitored.

Historically, foreign war volunteers, whether in Spain or in other conflicts, have never been homogeneous in terms of their motivations, commitment and postwar trajectories. Today, a measured approach by the authorities is therefore more likely to help deradicalise those former supporters of IS who have become disillusioned with the cause. Where there is evidence that returning fighters were involved in carrying out crimes while in Syria or that they pose a clear security threat and intend to carry out terrorist attacks after their return, they should certainly be prosecuted. This is certainly the case for the alleged members of the “Beatles” gang.

However, in instances where the security forces don’t see an imminent threat, programmes that aim to reintegrate disillusioned jihadists into society may be more productive in the long run than a heavy-handed approach. This would not only help such individuals escape from a cycle of violence but could also serve as a counter-narrative to the one promoted by extremists.

For instance, there are organisations such as the Institute for Strategic Dialogue that make use of networks of former extremists and survivors of violence in an attempt to deradicalise people who look as though they are beginning to drift towards dangerous organisations such as IS. This method does not replace law enforcement but could operate alongside it.