The UK Supreme Court ruled in the Dillon case against an interpretation that expanded the Irish Sea border's reach into legacy investigations from the Troubles. The decision overruled Northern Ireland's Court of Appeal.

The court rejected arguments from Irish nationalists, the Northern Ireland Human Rights Commission, and the Equality Commission for Northern Ireland. Those groups supported a broader application of the Windsor Framework to such cases.

The ruling also restricted how the European Court of Human Rights in Strasbourg applies to legacy probes in Northern Ireland. Republicans had sought to limit the Independent Commission for Information Retrieval and Recovery, or ICRIR.

ICRIR is led by Sir Declan Morgan, former lord chief justice of Northern Ireland. The commission was established by the previous Conservative government.

The Supreme Court dismissed efforts to undermine ICRIR. It noted uncertainty over a prior Tory amnesty proposal for Troubles killings, pending possible Strasbourg review.

The decision curbs Northern Ireland courts' role in expanding legacy investigations, which target security forces.