There is a neat symmetry to complaints from Aontú and the DUP about immigration.

Aontú wants the British and Irish governments to implement “an Irish sea border for people” to close what its leader, Peadar Tóibín, describes as “the open back door between both countries”.

Gavin Robinson, the DUP leader, believes the open back door is at the Border itself. He called this week for UK immigration officers to check trains and buses entering Northern Ireland from the Republic.

Both leaders have framed their calls as a defence of the Common Travel Area (CTA), saying they want to prevent people exploiting its vulnerabilities.

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Yet each has focused on a frontier within the CTA, at sea or on land, that happens to suit their republican or unionist perspective.

When considering immigration, the CTA is better understood and promoted as one frontier around the UK and Ireland.

We are increasingly bombarded with stories about the CTA’s failures in this regard but there was rare coverage on Tuesday of a........

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