The British government will not have time to introduce invisible customs arrangements on the Irish border before Brexit, an influential group of MPs warned.
Withdrawal is due in just over a year, and the Northern Ireland Affairs Committee said the UK may need to remain in or parallel to the customs union and single market throughout the two-year transition period.
They said ministers should develop an innovative system capable of delivering customs compliance without “ineffective and unworkable” physical infrastructure.
The committee inquiry failed to find a technical solution capable of avoiding a hard border anywhere else in the world.
Foreign Secretary Boris Johnson had suggested crossings of the frontier could be monitored by technology like travel between London boroughs.
Committee chairman Dr Andrew Murrison said: “It is now clear that a significant transition period is essential for the options in December’s Joint Report (EU-UK) to be worked though.
“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.”
The report also rejected any proposals for a customs border between Northern Ireland and the rest of the UK.
“This would create a costly barrier to trade with Northern Ireland’s largest market and would be incompatible with the spirit and intent of the Belfast/Good Friday Agreement,” it said.
The report from the committee – made up of five Conservatives, three DUP MPs, three Labour MPs and North Down independent unionist Lady Hermon – said the negotiating timeline made it “challenging” to expect full implementation of a new non-visible customs regime by March next year.
It added: “We have seen no evidence to suggest that, right now, an invisible border is possible.”
The committee heard “numerous” proposals for how the UK and the EU could ensure customs compliance without physical infrastructure, including mobile patrols, data sharing and enforcement measures away from the border.
“However, we have had no visibility of any technical solutions, anywhere in the world, beyond the aspirational, that would remove the need for physical infrastructure at the border.
“We recommend the government bring forward detailed proposals, without further delay, that set out how it will maintain an open and invisible border.”
Meanwhile, Tory MP Jacob Rees-Mogg has said that people claiming Brexit could lead to a return to the Troubles in Northern Ireland are “almost encouraging violence”.
He branded warnings that Brexit could pose a threat to peace in Northern Ireland as “cynical”, telling the Commons last night: “Once you start proposing that violence may be a consequence of something, you’re almost encouraging violence. So, people making that argument should think very carefully about the wisdom of that argument.”