The British government is setting up a new border zone in which military and customs officials would have extra powers to stop, search and interrogate people within a mile-wide strip across Ireland.

The powers are contained in a new "Counter-Terrorism and Border Security" Bill which is currently passing through the Westminster parliament in London.

If the bill becomes law, anyone could be detained and searched to establish if they are entering or leaving British jurisdiction, and their purpose in doing so, regardless of citizenship.

The new proposals have already passed committee stage at Westminster and the law could be in place by Christmas, well before Britain is scheduled to leave the European Union.

Under the proposed legislation an "examining officer" may question a person to determine if they are engaged in "hostile activity", defined to include anything which could be contrary to Britain's "economic well-being".

The new powers will also be applied at Newry train station, where passengers may be searched after they have crossed the border, as well as in some built-up areas of Strabane and Derry. The new legislation is to facilitate the new police-like Border Force, which will be deployed by early 2019. The existing PSNI relies on anti-terrorist legislation to stop members of the public.

Sinn Fein's Michelle O'Neill accused the British government of duplicity and 'clearly preparing for a hard border in Ireland'.

"The use of stop and search powers is already a cause of massive concern in nationalist areas and if powers as wide-ranging as these were introduced, it would be disastrous," she said.