Nicola Sturgeon has sensationally claimed Labour had a secret plan to drop its opposition to a second independence referendum.

The First Minister told a televised leaders' debate that Kezia Dugdale, the Scottish Labour leader, used to agree with her that Scots should get another vote on separation because of the Brexit vote.

She then disclosed details of a telephone conversation they held after the day after the EU referendum, in which she alleged Ms Dugdale said Brexit "changed everything" and Labour should no longer oppose an independence referendum.

The Labour leader vehemently denied the claim but the Scottish Tories said the allegation "holes Scottish Labour's entire campaign below the waterline."

Ms Dugdale's party has focused its campaign on promising to oppose a second independence referendum, but Ms Sturgeon's intervention could encourage Unionist voters to switch to the Conservatives.

Ms Sturgeon made the claim barely 24 hours before Scots go to the polls, with her party hemorrhaging votes to Labour, potentially threatening a series of SNP seats.

But Ms Dugdale faced heavy criticism last year for saying before the EU referendum it was "not inconceivable" she could back independence if there was a Brexit vote.