Kezia Dugdale has given the most forthright defence yet of her Unionist credentials as she rounded on Ruth Davidson amid polls showing the Scottish Conservatives could overtake Labour in next month’s Holyrood election.

In an interview with the Telegraph less than two weeks out from polling day, Ms Dugdale said she had “knocked my pan in” for two-and-a-half years during the independence referendum campaign and she was “proud to vote No.”

In contrast, the Scottish Labour leader said Ms Davidson was keen to “pour petrol” on the row over Scotland’s constitutional future and it was her Tory counterpart who “undermines the Union”.

Ms Dugdale also poured scorn on the Scottish Tory leader’s claim she could provide more effective opposition than Labour and insisted her party’s decision to oppose the renewal of Trident despite her support for the nuclear deterrent and that of the UK party – demonstrated her leadership qualities.

Speaking from the Edinburgh Eastern constituency she is contesting, she claimed that her party’s plan to use Holyrood’s new powers to increase income tax did not mean Labour had left the centre ground of Scottish politics because it was supported by the middle classes.

But another opinion poll yesterday showed Labour and the Conservatives neck-and-neck for second place, with the SNP far ahead and apparently on course for another majority.