DAVID Mundell is under growing pressure to resign as Scottish Secretary after other Tory ministers quit saying Theresa May’s Brexit deal threatened the Union.

Labour said it was “farcical” that Mr Mundell had given his backing to the draft withdrawal agreement, despite previously saying the integrity of the Union was paramount.

He and Scottish Tory leader Ruth Davidson reportedly threatened to resign last month if Northern Ireland was given a “special status”, which could now happen.

Resigning as Brexit Secretary this morning, Dominic Raab cited protection of the Union as his first consideration in leaving the government.

He said: “I believe that the regulatory regime proposed for Northern Ireland presents a very real threat to the integrity of the United Kingdom.”

Esther McVey quit as Work and Pensions Secretary.

She said Mrs May’s deal “threatens the integrity of the United Kingdom, which as a Unionist is a risk I cannot be party to.”

On Twitter, Nicola Sturgeon said: “I just hope that Esther McVey takes the travesty that is Universal Credit out the door with her.”

Shailesh Vara also resigned as minister for Northern Ireland with a warning about the “constitutional integrity” of the UK.

He said that pending exit from the proposed temporary customs union - which Brexiters fear with become indefinite - Northern Ireland would be “subject to a different relationship with the EU from the rest of the UK”.

He said: “Whilst I agree there should be no hard border between Northern Ireland and Ireland, the economic and constitutional integrity of the United Kingdom must be respected.”

Suella Braverman quit as Brexit minister - the second holder of the brief to quit.

She said the Irish backstop proposals “set out different regulatory regimes for Northern Ireland and Great Britain threatening to break up our precious Union.

“I am confident - having met with customs professionals in my role at the Department - that this could have been avoided.”

On Wednesday night, Mr Mundell said: “I was content to move to the next stage of the process on the basis that Brexit will deliver for our fishing industry – as I and colleagues set out in our letter – and on the basis that arrangements for Northern Ireland will not undermine the economic or constitutional integrity of the UK.”

Shadow Scotland Secretary Lesley Laird said: “It is farcical that the Brexit Secretary has resigned because the Prime Minister’s deal undermines the integrity of the UK, while the Scottish Tories stay silent. So much for standing up for Scotland's place in the UK.

“Ruth Davidson and David Mundell threatened to resign if the integrity of the UK was put at risk – and it appears Theresa May has simply ignored them. It’s clear this Tory government is a threat to the future of the UK.

“If David Mundell had a back bone then he would resign with immediate effect.

“We were promised that the Scottish Tories would be a strong block who would work in Scotland’s interests - what an absolute fallacy that has proven to be, they have been outmanoeuvred from the minute they arrived in London.”