It began last Friday, when Lord Empey attacked the DUP for its role in the December 2017 EU-UK “Joint Report”, saying the whole idea of a backstop stems from this document, and claiming the DUP is now trying to distance itself from a “time bomb” it helped create.

In the pages of Saturday’s News Letter, DUP MP Mr Wilson responded by saying: “What planet does that man live on?”

Whilst the DUP had not been able totally remove the idea of a backstop from the document said Mr Wilson, it nonetheless “thwarted” it by ensuring that a British government guarantee of “no new regulatory barriers” between NI and Great Britain was included.

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Sammy Wilson

Then today Lord Empey said whilst the DUP claimed credit for amending the Joint Report, “they did not reject it as they should have done”.

“Wake up Sammy,” he said. “I am on planet Earth, you are on planet DUP!”

The row all hinges on a couple of key paragraphs in the Joint Report, concerning what would happen with the border in the event no overall Brexit deal can be reached.

Sir Reg Empey

They are as follows:

“In the absence of agreed solutions the UK will maintain full alignment with those rules of the Internal Market and the Customs Union which, now or in the future, support North-South cooperation, the all-island economy, and the

protection of the 1998 Agreement.” (par 49)

And:

“In the absence of agreed solutions... the UK will ensure that no new regulatory barriers develop between NI and the rest of the UK” (par 50).

The DUP has effectively claimed credit for adding Paragraph 50 to the text.

Lord Empey said: “Even with the addition of the amendment which said there would be no border between GB and Northern Ireland, the December 8, 2017, document spells out two contradictory propositions.

“Northern Ireland cannot be in ‘regulatory alignment’ with Brussels and have no border with GB unless all of the UK is in the Customs Union.

“If we are still in the Customs Union, there is effectively no Brexit, something which Sammy wanted!

“To say that the DUP ‘thwarted the backstop’ is obviously nonsense.”

For his part, Mr Wilson has previously described the situation as contradictory.

“That’s why we’re now at the impasse that the prime minister signed up to the backstop, and we – using our position – made her sign up to an assurance that Northern Ireland would not be treated in the way which the EU wanted it to be treated,” he said.