The Mauritanian tells the true story of Mohamedou Ould Slahi, whose plight has left a stain on ideas of Anglo-American justice

I started work at Liberty, the civil rights advocacy group, the day before the September 11 attacks. I recall the feeling of doom: it is important to remember the devastating loss of life on that day – 3,000 people from all over the world – in an event that is now often subject to denialist conspiracy theories. Soon after, British ministers were contemplating far-reaching “security measures” against the background of fear that the same could happen in London. Surveying the entire population was a price worth paying, they said.

Having worked at the Home Office before joining Liberty, I knew the that way Britain treated migrants – who are subject to fewer protections than citizens – might well become the framework for the UK’s draconian approach to anyone suspected of terrorism. But I never predicted how long the post-9/11 legacy would linger. And with my Hollywood ideals of Anglo-American constitutional norms, reflected in movies such as A Few Good Men, I never imagined that the use of torture would become a systematic technique of interrogation.

Related: The UK government is attempting to bend the rules on torture | Nicholas Mercer

Lady Shami Chakrabarti was shadow attorney general for England and Wales from 2016 to 2020 and director of Liberty from 2003 to 2016

This post was originally published on Human rights | The Guardian.