I never thought I’d have to produce a passport travelling from London to Oxford. Until last week, that is. I was giving a talk at an Oxford college. “Bring your passport,” I was told. “The government has made employers legally responsible for ensuring that anyone who works for them has the right to do so. We need to see your passport before you can begin teaching.”

It was a shocking and outrageous demand and not one I’ve received from any other college, Oxford or otherwise, yet perfectly understandable within the context of the government’s “hostile environment” policy that has turned universities, hospitals, schools, landlords, employers, even homeless charities, into immigration police and created a climate of suspicion under which everyone is assumed to be guilty until they can prove themselves innocent.

To have to show a passport before giving a talk is a minor irritant. For many people, as the Windrush scandal exposed, and as EU citizens in post-Brexit Britain may find, such checks can be a life-changing experience, denying them hospital treatment or welfare benefits, even leading to detention or deportation.

When it comes to immigration, a nation’s border these days does not coincide with its geographical boundary. Border controls extend both inside the actual border and well beyond it, too. It extends inwards by insisting on internal checks on a nation’s population. The tighter the external controls, the more coercive the internal controls.

And it extends outwards, especially for rich western nations, by casting a net over neighbouring countries. The EU outsources immigration policing to myriad African and Middle Eastern nations, creating a new kidnap and detention industry throughout the region. American immigration controls reach out into Central and South America and the Caribbean.

From Oxford colleges to Sudanese prisons, the obsession with immigration is wrapping our lives in a web of suspicion and policing. I was merely inconvenienced. Others pay with their lives.

• Kenan Malik is an Observer columnist