The removal of a key piece of law will be 'litmus test' of any DUP deal to bring back Stormont - Allister

He also said “tinkering with processes” will not change the current reality.

Meanwhile, the former Labour minister Baroness Kate Hoey has told the News Letter that she hasn’t seen enough progress on the sea border for the DUP to return to Stormont.

Any deal between the DUP and government could focus on an enhanced green lane, with the architecture of the Windsor Framework remaining in place. This week the UK and EU met in Brussels to discuss implementation of the deal.

DUP leader Sir Jeffrey Donaldson has asked for changes to ‘unnecessary customs processes’ at the sea border – and suggested that the current green lane is neither “acceptable or practical”.

In an email to party members last week, Sir Jeffrey said the UK internal market scheme should be the “default route” for goods entering Northern Ireland from Great Britain. This scheme grants access to the green lane – and requires businesses moving goods between GB and NI to register.

The DUP is also seeking legislative changes to strengthen the Union. However, Mr Allister said that only restoration of the Act of Union will resolve the current political crisis.

He said: “Whatever else is desirable, this is the imperative, because it goes to the very heart of what the Union means and our place within it. There is no room to fudge this fundamental.”

The TUV leader said the Supreme Court showed that Article Six of Act of Union – the foundational document of the UK – is “in suspension” because Parliament passed Section 7A of the EU Withdrawal Act. “Only the repeal of section 7A can restore Article Six”, he said.

“Section 7A gave supremacy to the protocol and as it fetters trade from GB its supremacy put the guarantee in Article Six of unfettered trade into suspension. That is not just my opinion, but the finding of the highest court in the land.

“Consequently, any ‘deal’ which does not reverse section 7A will not restore Article Six and, therefore, not meet the fundamental unionist requirement. Nor, should anyone try and pretend otherwise.

“Tinkering with ‘processes’ will not alter the continuing reality of section 7A’s suspension of Article Six of the Acts of Union. What any ‘deal’ does with section 7A is the litmus test.”

The North Antrim MLA has also hit out at claims by the UK government to the News Letter that Northern Ireland is “legally and practically” in the UK’s customs territory.

The government said that on plant and animal health checks “the Windsor Framework disapplies the EU laws that applied under the old protocol so that food can once again be moved to NI and sold in shops on the basis of British food safety standards, not EU standards.”

Mr Allister said the Windsor Framework helped supermarkets – but little else.

“Everything else, if at the presumed risk of entering EU single market, is under the rigour of their customs code – which is not ameliorated by the affirmation of still being in UK customs territory. We may be in UK customs territory but we are subject to EU customs code,” he said.

Baroness Hoey of Lylehill and Rathlin – who will question Foreign Secretary Lord Cameron on the Windsor Framework in the Lords next week – said she hasn’t see anything that would make her confident that Stormont will be restored in the near future.

“Government has to first accept that the Windsor Framework needs to go, and renegotiate with the EU. Going back into the executive without a proper restoration of Article Six of the Act of Union would mean the DUP reneging on their promises – and I can't see Sir Jeffrey doing that,” she said.

The DUP said it is “working to restore our place in the Union and its internal market and thus protect our Article Six economic rights as an integral part of the UK”.

The party said as a result of its actions it is making progress and is “determined to secure a good deal for NI”.