Renu Begum, eldest sister of Shamima Begum, 15, holds her sister's photo as she is interviewed by the media at New Scotland Yard, London, England, February 22, 2015.

© 2015 Laura Lean/WPA Pool/Getty Images

“All I want to do is come home to Britain.”

So says Shamima Begum, a heavily pregnant British teenager, who joined the Islamic State aged 15 but last week fled as ISIS’ final stronghold in eastern Syria crumbled around her.

Her case has sparked heated debate about how those who moved voluntarily to live under ISIS rule should be treated by their country of citizenship.

Now that the ISIS caliphate is no more, we can expect more young women like Begum, who is now 19, and their children born under ISIS rule, asking to come home. These cases inevitably raise uncomfortable questions.

But nevertheless, there are certain laws and principles that should guide public debate.

Firstly, the UK government should not block a citizen’s return home, as the UK’s security minister has acknowledged. While the British government is not obliged to “rescue” Begum from the camp where she is being held, the UK government’s offer of consular assistance only if Begum makes her own way to a place outside Syria isn’t much of a solution, not least because Begum is not allowed to leave the camp she is in. In addition, the authorities currently holding Begum are allies of the UK, and other countries, including the US, have helped their nationals return from Syria.

Secondly, if there are grounds to believe a Briton has committed a serious crime during their life under ISIS, it’s in the interest of the UK government to ensure they are investigated – in line with international standards – and prosecuted if appropriate, taking into account their age and all other relevant circumstances.

Authorities in northern Syria have repeatedly indicated that they don’t want to prosecute foreigners. So if the UK government wants justice for victims of ISIS’ murderous rule, it should allow possible perpetrators home and let British justice decide on their guilt or innocence.

Headlines about “jihadi brides” returning home inevitably provoke strong emotions. But one thing is clear: the UK’s responsibility for its citizens does not end at the cliffs of Dover.