When Isis comes home

The Islamic State’s pretence to nationhood was based on the holding of territory. With the battle for Mosul this week, together with the loss of the land that it controlled in Syria, that pretence is becoming harder to maintain. The area involved is now limited to a few shattered cities, and corridors between them.

The decline of this terror organisation is to be welcomed. But this is a war which can have no neat ending. If Isis were a genuine state, it would by now be forced to consider unconditional surrender. That is not going to happen. More probably it will dissolve, its leaders and lesser agents making an escape or going into hiding.

There is a danger that many Isis fighters will attempt to return to the European cities from which they came and continue an underground jihad. According to the EU security commissioner, 2,500 Europeans are in Isis-controlled territory. Some 850 UK citizens are understood to have travelled there, of whom 450 remain.

We must not be naive about the threat these people pose. While no doubt some have had a genuine change of heart and will abandon religious extremism, it is certain that others have not and will continue to plot acts of terror.

Were Isis a real state, every British citizen who travelled to fight for it would be guilty of treason. As things are, the government has struggled to decide what to do with returning jihadists. When, two years ago, the then Prime Minister David Cameron suggested removing their citizenship, the idea was immediately shot down because it would have rendered them stateless.

Instead, a weaker measure went into the Counter Terrorism Act: British citizens who join terror groups can have their passports seized and be prevented from re-entering the country for up to two years other than on terms stipulated by the Home Secretary.