Under fierce questioning, the prime minister declined – four times – to explain how her “facilitated customs arrangement” will work, even as she seeks agreement in Brussels.
Asked repeatedly if payments would have to be collected at borders – something the EU is expected to reject – she would go no further than the need to agree a “tariff revenue formula”.
Several times, Ms May said that “what matters is what money comes to the United Kingdom”, eventually suggesting it was a matter for the negotiations.
At one point, a flustered prime minister referred mistakenly to a “future customs arrangement” and a “facilitated customs agreement”.
Yvette Cooper, the Labour chairwoman of the Commons home affairs committee, went on the attack, saying: “I’m really baffled as to what’s going to happen.”
She said: “Don’t you have a problem that you are not being straight about the language and about what it is you are actually proposing?
“So, everybody is confused and, as a result, no one trusts what the government is doing.”
On the suggestion that her proposals were “baffling”, the prime minister said: “I’m not sure what is baffling about us exchanging sums of money that are relevant to both parties.”
During an exchange lasting ten minutes, Ms May did make clear that the plan would not involve “someone physically handing cash over at the border”.
Giving evidence to the heads of all Commons committees, Ms May also admitted that only the “majority” of the plan would be ready for December 2020, the end of her proposed transition period.
And, asked to identify where else in the world such a complex system already exists, she replied: “It doesn’t – it’s a novel idea.”
The customs plan, unveiled at Chequers a fortnight ago, promises tracking technology to allow the UK to collect, and pass on, the tariffs on goods destined for the EU.
However, after she caved in to demands from the hardline European Research Group (ERG), that will now be “illegal” unless the EU also collects duties for the UK.
Ms Cooper said the issue of collection at EU borders would arise if the UK ended up with higher tariffs than the EU for goods imported from some countries.
Earlier, Ms May said only the “majority” of the plan would be ready for the end of the 21-month transition she is seeking, after the UK leaves the EU next March.
“There is a question as to the speed with which the repayment mechanism would be in place,” she admitted.
“So far, the suggestion is that could take longer to be put into place. That has yet to be finally determined.”
Sarah Wollaston, the Conservative chairwoman of the health committee, urged her to be “transparent” with the public about what they needed to do to prepare for a no deal.
Her committee had heard evidence that people with long-term health conditions would be uninsurable in those circumstances, she warned.
The prime minister said the government would be issuing technical notices to people working in specific areas – while insisting a deal was still possible by October.
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