Keir Starmer must stop people-smugglers using Northern Ireland as a back door into Britain, senior unionists have warned.

They fear that migrants will increasingly abuse the open border with Ireland if Sir Keir’s “one in, one out” deal with Emmanuel Macron drives down migrant Channel crossings.

The UK and Ireland share a common travel area, which predates both countries’ EU membership and allows free movement for British and Irish citizens.

The “Irish route” sees migrants fly to Dublin from Europe, either legally or on false papers, before travelling unchecked to Northern Ireland by land.

Once in the UK, it is possible for them to claim asylum. It is also possible to travel to Britain without a passport, although airlines and ferry operators do ask for photo ID.

“We will be telling the Government to closely monitor the flow of people and do what is necessary to protect and defend the entire border of the UK,” Lord Dodds, the Democratic Unionist Party peer, told The Telegraph.

A Telegraph investigation last month revealed that Albanian gangs were charging £4,000 to use the soft border to get people into Britain, and advertising the scam on Facebook.

The gangs give migrants fake Italian ID cards that are used to fly them into Ireland, before they sneak into mainland Britain on ferries, allowing them to work illegally or claim asylum with their Albanian passports.