Sajid Javid, the home secretary, and Jeremy Hunt, the foreign secretary, have ordered officials to make preparations for a war crimes trial modelled on those in Rwanda. Under the plans, the government would pay “large sums” to the Iraqi government to try to jail British nationals and prevent them from being freed to launch terrorist atrocities on home soil.

About 900 Britons travelled to the region to join IS with half returning home. Ministers regard those who have been captured as a security risk but do not want to put them on trial in the UK because of various difficulties.

Earlier, Iraq had offered to try hundreds of foreign IS suspects currently being held in Syria in return for millions of pounds, according to reports.

Iraqi officials last week made the proposal to the US-led coalition that it would put the detainees on trial in Baghdad if they received $2million (£1.5m) per head per year, sources told AFP.

One of the sources said the calculation was based on the estimated operational costs of holding a detainee in US-run Guantanamo prison.

Around 1,000 suspected foreign IS fighters are in detention centres in northeast Syria run by the US-backed Syrian democratic Forces (SDF), in addition to around 9,000 foreign women and children in camps there.

There are at least 26 British men and women and around 30 children in SDF custody.

The Kurdish-led forces say they do not have the facilities or resources to hold them indefinitely. There are also a number of pressing security fears after a riot in one of the main prisons last week.