THE SNP's inability to rule out a second bid for independence is a bigger uncertainty for Scotland than the EU referendum, David Mundell has insisted as he called on the Nationalists to “stop obsessing” about another poll.

The Scottish Secretary argued that June's vote on Britain's membership of the EU should not be a "re-run" of the 2014 independence referendum.

He told MPs that Nicola Sturgeon must rule out the prospect of a second poll if she was returned as First Minister.

Earlier this week, David Cameron played the Union card in the starkest terms yet, warning that Brexit could lead to the "disintegration" of the UK.

Ms Sturgeon has made clear that she believes there will be an ''almost certain'' drive for another independence referendum north of the border if Scotland voted to stay in the EU but England voted to leave.

Speaking in the Commons, Mr Mundell replied to a raft of SNP questions about the EU referendum by referring to a second independence vote.

After the Nationalist MP Patricia Gibson, who represents North Ayrshire and Arran, urged the UK Government to ditch Project Fear and make the positive case for staying in the EU, Mr Mundell said: "You and your colleagues repeatedly call for a positive campaign for Scotland to remain in the EU but all we hear about from them is process and calls for a second referendum.

"I call on them to disregard that approach and actually start setting out the positive case themselves," declared the Secretary of State.

He told Gavin Newlands, the SNP MP for Paisley and Renfrewshire North: "The biggest issue that faces Scotland currently is the uncertainty over the Scottish Government's inability to rule out a second independence referendum, which they could quite easily do.

"I look forward to the First Minister, if she is re-elected to that post, setting out clearly that we aren't going to have a second independence referendum."

Mike Weir, the Nationalists’ chief whip wondered if Mr Mundell's "mission is to antagonise as many Scots as possible before the[EU] referendum".

Labour’s Ian Murray claimed the SNP was "desperate for any excuse to trigger another independence referendum".

Angus Robertson, the SNP leader at Westminster, said Scottish voters had returned a "pro-European SNP government" at Holyrood and urged the Tory Government to “concentrate please on making a positive and inspiring case to stay rather than re-warming endless scare stories".

Mr Mundell replied: "That's exactly what my intention is and perhaps you could undertake today to stop obsessing about process and a second Scottish independence referendum and concentrate yourself entirely on the positive reasons for Scotland remaining in the EU."

Meantime, Anna Soubry, the Business minister, praised the performance of the Scottish Tories in the Holyrood elections telling MPs: “I pay handsome tribute to the outstanding Ruth Davidson. Like the Prime Minister, she is a moderate, sensible, One Nation Conservative. She has turned the skies of Scotland blue with, if I may say, a rather pleasing tinge of pink at the edges.”