Scottish Secretary David Mundell branded the outgoing Brexit secretary a "carpetbagger" as he was urged to quit the cabinet.

Mundell said Dominic Rabb's resignation was "about manoeuvring and leadership" and denied speculation he would step down.

But the First Minister Nicola Sturgeon said he would do so if he had "backbone".

Rabb and pensions secretary Esther McVey said the proposals threatened the future of the UK as they made separate allowances for Northern Ireland.

Sturgeon recalled how both he and the Scottish Conservative leader Ruth Davidson - who is currently on maternity leave - said last month they would quit their posts if the Brexit deal threatened to undermine the "integrity of the UK".

She said: "Having chosen that red line, and they chose it, it is really, really hard to see how they stay in office after today with a shred of credibility.

"Let me quote the letter from David Mundell and Ruth Davidson just a few weeks ago. 'Any deal that undermines the integrity of the UK internal market or of the United Kingdom', that was the red line they were briefing.

"Then today you have got Dominic Raab, the Brexit secretary who has been involved in these negotiations, being very clear 'this deal presents a very real threat to the integrity of the United Kingdom', Esther McVey saying the exact same thing."

Ms Sturgeon, speaking at First Minister's Questions in Holyrood, added: "What is absolutely unclear to me is how David Mundell or Ruth Davidson can have any other option but to follow through on the principled commitment that they made.

"Let's see over the course of today, do they have any principle? Do they have a backbone between them? I suspect that answer is going to be a resounding 'no'."

Drama has engulfed UK politics since Prime Minister Theresa May announced her terms of a deal to leave the EU on Wednesday night.

Several ministers have resigned from the cabinet, including Rabb.

Mundell told ITV Borders: "I'm not taking lessons in standing up for our United Kingdom from carpetbaggers.

"Only a couple of years ago Dominic Raab was proposing to introduce a bill of rights into Scotland which would have overridden the Scottish legal system and devolution.

"So I'm not impressed by his latter-day commitment to the Union. I'm sure this is more about manoeuvring and leadership."

Mr Mundell added that he was "absolutely committed to the integrity on the UK" and said at Cabinet he would need to understand in greater detail the parts of the deal relating to Northern Ireland, which he said ran to 150 pages.

He said: "I believe that the best way of keeping the United Kingdom together is to ensure that we have a deal as we leave the EU, that Brexit delivers for Scotland and the rest of the UK and that is what I am focused on, not being part of some sort of soap opera of resignations and I am not going to be bounced into resigning by carpetbaggers."