For nearly 20 years, the Commonwealth operated under the mistaken assumption that it was allowed to hold people in immigration detention indefinitely. In 2023, the High Court’s landmark ruling confirmed otherwise.

We are now about to see the fallout of those events, with the government facing potential civil liability to people who, as it turns out, were unlawfully detained.

A new High Court judgment in a case called Abdel-Hady vs the Commonwealth has left the door open for a man who was unlawfully detained to sue the government for compensation, potentially allowing hundreds of others to do the same.

The legal history traces back to a 2004 High Court case. That case found that the Migration Act allows the government to detain unlawful non-citizens until they were deported, even if there was no realistic prospect of deportation (for example, if no other country would accept them).

For a person who had nowhere else to go, this effectively led to indefinite detention.

In a 2023 decision, often dubbed the NZYQ case, the High Court reopened and overruled that earlier case on constitutional grounds. The upshot was that the government had, for some time, been relying on an invalid law to detain a person where there was no foreseeable prospect of deporting them.

Without legal authority to detain, the Commonwealth faces potential liability for false imprisonment. This tort (a civil wrong) provides compensation if a........

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