Alistair Darling refused to endorse Jeremy Corbyn as he hinted the Labour leader will not last beyond the general election.
Campaigning in the party’s only Westminster constituency north of the border, the former Chancellor of the Exchequer also said Scotland is being left to “wallow in uncertainty” by the SNP’s agitation for another independence referendum.
Asked if he would back Mr Corbyn, Lord Darling said the London MP is leader “right up until the general election”, before adding that leaders “come and go”.
The Labour grandee was meeting activists in Edinburgh South on the 20-year anniversary of the party’s historic sweep to power under Tony Blair.
Ian Murray, who quit as Scottish Secretary over Mr Corbyn’s leadership, is defending the seat, where he has one of the smallest majorities in Scotland, amid fears the party will suffer a wipe-out north of the border on June 8.
Labour won 41 seats in Scotland in 2010, but could only keep hold of Mr Murray’s seat in the ballot five years later.
Lord Darling was asked by journalists in a Bruntsfield boulangerie on Monday if he would endorse Mr Corbyn.
“He is the leader, he is the leader for the next, right up until the general election,” he replied.
“You know where I stand on that, but my view is that we need to get on fighting the general election campaign.
“You know leaders come and go.
“It’s important we get the best possible result for the country and that means having a sensible, sizeable opposition – members of a government that can actually make a difference.”
The Better Together leader, who said he would not want to take on the role again in a re-run of the independence vote, said the economy was being stifled by the threat of another referendum.
“You have a choice in politics, you either create a positive platform where people feel confident they can invest in the long term because of they are not worried about where Scotland is likely to stand in the future, or you wallow in uncertainty, which is happening in the present time,” he said.
Lord Darling also warned that Tory Brexiteers are “hijacking” the debate over the UK’s future relationship with the EU.
“In this general election, voting Labour will prevent our country’s future being hijacked by Tory Brexiteers,” he said.
“And voting Labour will send a message to Nicola Sturgeon that the people of Scotland don’t want another divisive independence referendum.
“We made our decision in 2014 and we are stronger as part of the UK.”
An SNP spokeswoman said: “While the Labour party is expected to almost disappear into political oblivion at the general election, it is only a vote for the SNP that can stop the Tories and ensure Scotland’s voice is heard in Westminster.”