Theresa May has moved to postpone a second independence referendum indefinitely after refusing to set out the specific criteria Nicola Sturgeon must meet to justify another vote.

The Prime Minister, Ruth Davidson and David Mundell repeatedly refused to be pinned down on how Ms Sturgeon would meet the Tory manifesto’s key test that there would not be another vote without “public consent.”

Ms Davidson, the Scottish Tory leader, shied away from her previous suggestion that consistent 60 per cent support in the polls for another referendum would suffice, instead citing the political unanimity for the 2014 vote as the “gold standard.”

Neither would they provide any detail on the manifesto’s refusal to countenance a referendum “until the Brexit process has played out”, with Mr Mundell saying he did not know how long this would take.

However, the Scottish Secretary admitted this may rule out an independence vote before the 2021 Holyrood election. This would force Ms Sturgeon to put an unequivocal promise of another referendum before the Scottish people and seek a clear mandate, an extremely difficult task.