Hundreds of Islamic State terrorists are walking free in the UK because of a failure to prosecute them. An estimated 425 “fighters” have returned to Britain after committing horrific crimes in Syria and Iraq but an inquiry warned that none have been successfully prosecuted.

MPs and members of the House of Lords are now calling for new legislation so that they can be brought to justice. They said the Government should amend the Crime and Policing Bill, currently making its way through Parliament, to make prosecutions possible. Lord David Alton, Chair of the Joint Committee on Human Rights, said: “This is not something the UK can simply wash its hands of because it happened overseas.”

Islamic State, also known as Daesh, has committed crimes including murder and rape targeting religious minorities such as the Yazidis, a religious minority which has faced persecution for centuries. An estimated 5,000 Yazidis have killed and more than 200,000 displaced from their homes.

Lord Alton said: “We know that British nationals committed the most horrendous crimes in Iraq and Syria under the Daesh regime and we have a duty to see them brought to justice. To date, no Daesh fighters have been successfully prosecuted for international crimes in the UK and we find this unacceptable.

“We want to see more action from the Government in identifying the perpetrators, some of whom may have returned to Britain, others likely detained in camps in Syria. This will require better coordination from law enforcement and criminal justice, and also the removal of barriers preventing some prosecutions.”

Some may have gone free because of a legal loophole which means it is not possible for British courts to prosecute people for genocide, crimes against humanity or other war crimes committed abroad, unless they are UK nationals, UK residents or subject to laws which apply to members of the armed forces.

While no official figures exist for the number of Islamic State terrorists in the UK, the Government has estimated that 850 people left the country to join the extremist group in Syria and Iraq, and around half are believed to have returned.

But the Joint Committee warned: “The UK Government has formally recognised that the acts committed against the Yazidi people by Daesh were acts of genocide. However, despite this recognition, there have been no successful prosecutions of Daesh fighters in the UK for international crimes, including genocide.

“To remedy this concerning reality, we recommend several changes to policy and law to achieve greater accountability of Daesh fighters for their crimes.”

It also urged the Government to step up efforts to identify British citizens held in camps in Syria so that they can be returned home and prosecuted. Around 42,500 ISIS terrorists and family members are held in what are effectively giant prison camps and these are thought to include 20 British households, including children.

The inquiry called for more oversight of decisions to remove British citizenship from people who are thought to be a threat to the public. The UK can do this when a person will not be left stateless as a result, for example if they have dual citizenship, and the most high-profile case is that of Shamima Begum, a UK-born woman who travelled to Syria in February 2015, aged 15, where she married a Daesh fighter. She was deprived of her citizenship four years later.

However there are many examples that receive little publicity and between 2010 to 2023 at least 1,080 deprivation of citizenship orders were made.

The Committee said: "The Government must provide greater transparency as to the use of deprivation of citizenship powers, including by providing regularly updated data to the public.”

A Government spokesperson said: “The Government’s priority remains maintaining the safety and security of the UK and we are committed to achieving accountability for all victims of Daesh’s crimes.
“We will consider the findings of this report.”