Security sources told the newspaper that Government officials are working on a mechanism to prevent EU citizens using Ireland to “sneak into Britain” after Brexit.

One “senior security source” said: “We will need to have a mechanism that restricts the freedom of movement of a person like that travelling to the Republic with the intention of travelling on to Britain.”

Meanwhile, another Government source said: “We are looking at developing watch lists. People on these lists would be strictly not permitted to enter Britain.

“And while all the benefits of the Common Travel Area between Britain and Ireland would continue after Brexit, we need a mechanism to ensure people banned from Britain can’t use the Common Travel Area as a way around that ban.”