Brandon Lewis was challenged to set out under which part of the Northern Ireland Protocol the incendiary unilateral action falls – amid claims it will breach international law.
“Is it Article 16, which allows the UK to unilaterally take appropriate safeguard measures? And, if not, which other article is he citing?” Labour’s Hilary Benn asked.
But – despite repeatedly insisting the government is acting “lawfully” – Mr Lewis was unable to point to any part of the Protocol that allows it.
In the Commons, he repeated his warning that Northern Ireland was faced with “empty shelves, potentially, in just a couple of weeks’ time”, if the action had not been taken last week.
And he lashed out at Labour for “defending the EU rather than defending the actions of the UK government, which is standing up for the people of Northern Ireland”.
Mr Lewis insisted London is keen to get back round the table with the EU, to reach agreement on extending ‘grace periods’ before the checks are introduced.
However, the failure to set out the basis for unilaterally delaying the checks is likely to be seized upon, as Brussels prepares to take its legal action.
That is likely to include a formal “infringement proceeding” that could end up at the European Court of justice, as well as triggering the dispute mechanism in the Brexit withdrawal agreement.
EU27 ambassadors are said to be in full agreement that the EU “had to act firmly” and action could begin as early this week.
The checks on goods from Britain were agreed to avoid a hard border with the Irish Republic, as the EU seeks to protect the integrity of its single market.
But the UK suddenly aborted their introduction, having failed to persuade Brussels to delay them until 2023, an agreement the Protocol requires.
Facing an urgent question – and Unionist demands to scrap the agreement altogether – Mr Lewis told MPs: “We are a very trustworthy partner.”
And, in reply to Mr Benn, he blamed Brussels for inflaming “issues and tensions” by briefly threatening to invoke Article 16 itself, in the row over vaccine exports.
“The measures I announced last Wednesday are lawful and consistent with the progressive and good faith implementation of the Protocol,” he said.
And he added: “They do not change our legal obligations as set out in the Protocol under any of its articles.
“These measures are of a kind well precedented in the context of trade practice internationally and are consistent with our intention to discharge our obligations under the Protocol in good faith.”
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