There is no way to avoid a hard border in Northern Ireland after Brexit under the government's current proposals for solving the issue, MPs have said.
A report by the Northern Ireland Affairs Select Committee said there were no examples “anywhere in the world” that show the invisible border promised by ministers will be feasible.
The cross-party group of MPs called on the government to clarify how it intends to keep the border open in line with the promises of the Good Friday Agreement.
They said Northern Ireland would have to maintain full alignment with EU rules and tariffs during any Brexit transition period to allow time for a new system to be developed.
The vexed issue of keeping the border between Ireland and Northern Ireland fully open after Brexit has become a major headache for ministers undertaking the negotiations.
Foreign Secretary Boris Johnson has suggested a London congestion charge-type system could solve the problem – but has also admitted in private that the border may need some physical infrastructure.
In its new report, the Northern Ireland Affairs Committee said it had seen no technical solutions anywhere across the globe “that would remove the need for physical infrastructure at the border”.
It added: “We have seen no evidence to suggest that, right now, an invisible border is possible.”
Chair of the committee and Conservative MP Dr Andrew Murrison said a “significant transition period is essential” for the aims agreed by the EU and the UK in December to be worked out.
“It is equally clear that regulatory and tariff alignment will be required during transition to avoid any hardening of the border before a definitive low-friction solution can be determined,” he added.
Brussels has said Northern Ireland could remain in the customs union after Brexit to solve the problem – effectively creating a new border with the rest of the UK at the Irish sea.
But the government – and the DUP, whose 10 MPs prop up Theresa May in her minority administration – have ruled the option out.