Scottish Labour would not join forces with the Conservatives in a joint campaign to defend the United Kingdom if Scotland held a second independence referendum, leader Kezia Dugdale has said.
Momentum toward a new vote is growing, with Britain's impending exit from the European Union feeding secession demands.
Dugdale, whose party rejects Scottish independence, told a meeting at the party conference in Aberdeen she could "not imagine" leading Scottish Labour into a joint campaign with the Conservatives like the 2014 "Better Together" campaign which defended the union, a Scottish Labour official said.
Despite beating Scottish secession by a 10-point margin in the 2014 referendum, that alliance of historic rivals Labour and Conservatives was consumed with infighting and ended up discrediting many of those involved.
The Scottish referendum was then followed by a historic win for Nicola Sturgeon's Scottish National Party (SNP) the following year. It now has 54 of 59 seats representing Scotland in the British parliament in London, taking share mainly from Scottish Labour, which has seen its support slump.
It would be "a mistake" for the head of the Scottish Conservatives, Ruth Davidson, to lead any such new referendum campaign, Dugdale also said. Some politicians have cautioned about the potential hazards of Conservatives, in power in London, giving the impression of telling Scotland what to do.
Dugdale will tell delegates at the Scottish Labour conference the party doesn't want another referendum which could break up the three-century-old union of England and Scotland.
"The unfortunate truth is this: with the SNP supported by the Greens, they have a majority in the Scottish Parliament. So if this country faces another referendum at any point in the future, I will work tirelessly to make sure that our side of the argument is successful again," she is to say.
Scotland, one of the UK's four nations, voted overwhelmingly to stay inside the EU in last June's Brexit referendum but will nevertheless leave because the UK as a whole voted to do so.
British Prime Minister Theresa May plans to trigger the two-year process next month.
That means independence should continue to be an option, the SNP argues.