Moral principles are rarely verified by easy cases. It’s the difficult ones, the ones that cause most debate and hostility, which truly test the moral mettle.

Consider the question of citizenship. Most people would agree that members of the Windrush generation – Caribbean migrants who came to Britain as children or were born here – are British citizens, even if they don’t have a piece of paper to prove it.

The attempt to deport a group as “foreign criminals” provides a harder test. The government claims that as criminals the deportees have no right to stay. Had they not committed a crime, many would have been regarded as British even without documentation. The fact of their crime should not change that moral principle.

Or take the most difficult cases of all – those relating to British terrorists. Last week, jihadist bride Shamima Begum lost her first appeal against the revocation of her citizenship. A special immigration appeals commission accepted that revocation was legal as she could be “a citizen of Bangladesh by descent”.

Most will think it right that Begum be stripped of her citizenship because of her support for Islamic State. The real issue, however, is not about what Begum did or believed. It’s about Britain and its moral responsibilities. She is a British citizen. However terrible the acts she may have committed, she remains Britain’s responsibility, not the responsibility of the Kurdish forces who hold her, nor of Bangladesh, the country of her parents’ birth.

A year ago, I observed that politicians often claim that “what separates a nation such as Britain from the barbarism of Isis” is “its humane values” and that “it’s in these hard cases that we will discover how true that is”. That is still the case today.

• Kenan Malik is an Observer columnist