DAVID Mundell refused to resign yesterday despite seemingly accepting that Theresa May’s Brexit deal has crossed his red line on Northern Ireland.

Speaking on the BBC’s Sunday Politics Scotland, the Secretary of State for Scotland said he supported the Prime Minister’s deal as the alternative was “chaos”.

In October, he and Scottish Tory leader Ruth Davidson warned May that they could not accept any deal which “creates a border of any kind in the Irish Sea” or “leads to Northern Ireland having a different relationship with the EU than the rest of the UK, beyond what currently exists”

Legal advice given to Cabinet by Attorney General Geoffrey Cox, and released by the government in full last week, made clear that if the backstop was to come into force, then Northern Ireland would have to, in effect, treat the UK as “third country.”

Yesterday he said the “principle issue” was “the threat to the integrity of the United Kingdom”.

He added: “I have had to make a judgment on what is in the backstop, which is a temporary measure which may never come into force, and what risk that causes to the integrity of the United Kingdom, compared to crashing out of the EU in less than four months time, which I regard as the most significant threat to the integrity of the United Kingdom.”

Mundell also threatened to resign again, saying he could not serve in Boris Johnson’s Cabinet.