Labour MP Douglas Alexander has warned the party in Scotland it must reconnect with voters to compete with the SNP after its "bad beating" in May's election.
In a keynote lecture to be delivered at the University of Stirling, the shadow foreign secretary will say the party needs to "re-engage" to attract people back.
Mr Alexander will argue the party was seen by the public as concerned with "opposition for its own sake" without outlining a "clear enough alternative story".
The Holyrood election saw the SNP pick up nominally safe Labour seats, leading to an unprecedented majority in the Scottish Parliament.
Mr Alexander was at the centre of the "Divorce is an expensive business" anti-independence campaign which helped defeat the SNP in the 1999 election.
However, he will use the annual Andrew John Williamson Memorial Lecture to say times have changed and Scottish Labour can no longer campaign on negative messages.
He said he still believed independence was not the best future for the country but that the party failed, post-1999, to "draw a compelling enough picture" of the alternative vision.
He said: "It's hardly a surprise to admit that Labour took a bad beating back in May. We got one in eight votes from the Scottish people.
"So, I think the right response in the face of a defeat that was a significant one is of course to show humility, to listen, to reflect, to think and to try and re-engage."
The MP for Paisley and Renfrewshire South said he was more interested in using the lecture to set out the way forward for Scottish Labour.