David Davis has been mocked for coming up with "fantastical" solutions to the Irish border row after it emerged the government is considering a "buffer zone" between Northern Ireland and the Republic.
Pro-EU MPs accused the government of "making it up as they go along" as reports suggested the Brexit secretary was drawing up plans for a 10-mile area around the 310-mile border, under which local traders could operate under both UK and EU rules at the same time.
The Department for Exiting the EU (DexEU) declined to comment directly on the plans but confirmed that work was underway to refine post-Brexit customs options.
Ministers are under pressure to come up with a solution to the thorny issue of future customs arrangements on the island of Ireland amid fears that new infrastructure on the border could lead to a return to violence.
Theresa May's cabinet is split down the middle between the prime minister's preferred "customs partnership", where the UK would collect tariffs on behalf of the EU, and the Brexiteers favoured "maximum facilitation" solution, where technology is deployed to avoid border checks.
Both options have already been dismissed by Brussels and pressure is mounting on the government to agree a position before a crunch EU summit later this month.
Whitehall officials are drawing up up a new plan based on Lichtenstein's "double-hatted" model, which would allow Northern Ireland to use the same trade rules as south of the border, The Sun reported.
"They [the government] are desperate for any solution, no matter how fantastical, to appease Tory right wingers," said Labour MP Virendra Sharma, who supports the pro-EU Best for Britain campaign.
"Even though it doesn't pass basic scrutiny they don't seem to care.
"Jacob Rees-Mogg is calling the shots at the moment and the Government are just doing his bidding."
His concern was echoed by Labour former shadow chancellor Chris Leslie, who said the only solution to the customs dilemma was keeping the whole of the UK in the single market and the customs union.
Mr Leslie, who backs the Open Britain group, said: "David Davis's new idea for solving the Northern Ireland border problem manages to combine a lack of feasibility with a complete ignorance of the history of the region. It is both dangerous and impractical."
Sinn Fein accused Mr Davis of trying to "hide a hard border in a buffer zone".
MEP Martina Anderson said: "Once again this shows the lack of knowledge of border areas and the concerns they face - David Davis obviously didn't learn much on his flying visits."
Ms May has split her top team into two working groups to consider both proposals and Mr Davis is leading efforts to consider "max fac", where technology such as automatic numberplate recognition would be considered to ensure goods can move freely across the border.
A Whitehall source told The Sun: “Max fac doesn’t look like anything it used to for Northern Ireland now, because the technology has been stripped out.
“But it doesn’t matter what we call it as long as it works, and we think it will.”
The source said the new plan was "tremendously complicated" but could unite the cabinet, although it would be a challenge to secure the backing of Ms May's DUP allies, who have made it clear that Northern Ireland must be treated the same as the rest of the UK.
A DexEU spokesperson said: “We have set out two viable future customs arrangements with the EU and work is ongoing to refine these.
"Both of these would deliver on our commitments to ensure UK-EU trade is as frictionless as possible, avoid a hard border between Northern Ireland and Ireland, preserve the integrity of the UK’s internal market and enable us to establish an independent international trade policy.”
A Downing Street spokesman said: "The Prime Minister has been absolutely clear that we cannot and will not accept a customs border down the Irish Sea, and that we will preserve the integrity of the UK's common market.
"Work is ongoing on customs plans that will achieve this, as well as ensuring we can strike trade deals around the world, that trade remains as frictionless as possible, and that there is no hard border between Northern Ireland and Ireland."
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