Dennis Canavan added that the Scottish Government must act now to increase pressure on Westminster to secure another vote on the constitution before the next parliamentary elections in 2021.
In an interview with Scotland on Sunday, the former Labour MP said he expected Nicola Sturgeon to give “a strong indication” shortly as to when she wants a second referendum to be held.
The prospect of indyref2 was ramped up at Holyrood last week when Greens co-leader Patrick Harvie urged the First Minister to “give Scots their own way out” of the Brexit crisis engulfing Westminster.
Sturgeon replied she would wait for clarity on the issue in the coming days before making an announcement on the potential route to another referendum. She added: “Nobody can be in any doubt that change is needed. The last three years have shown that the status quo is broken.”
Canavan insisted there was no time to waste on the matter. Asked how the Scottish Government should respond if, as expected, the UK government refuses to grant the legal powers to hold a second vote, he said: “It would not be wise at this stage to give advance notice to the enemies of independence about the best tactical response in the event of the UK government refusing an official request for a Section 30 order.
“The immediate priority should be to maximise pressure on the UK government to respond positively to such a request and to warn them of the consequences if they refuse. They must be made to realise that failure to respect a democratic mandate will provoke a constitutional crisis.
“Such a scenario would recruit more and more people into the independence movement and turn the next Scottish Parliament elections into a referendum on independence, leading to a landslide victory for supporters of independence.
“That would greatly reinforce the existing mandate and make it virtually impossible for any UK government to continue denying the democratic wishes of the people of Scotland.”
Prime Minister Theresa May’s embattled administration has already indicated it would not grant the Section 30 order that would be needed to make any referendum legally binding.
Foreign Secretary Jeremy Hunt told an audience in Glasgow earlier this month that if the Scottish Government were to ask for such an order, the answer would be a firm “no”.
Canavan was a leading figure in the 2014 Yes campaign, chairing its advisory committee and making regular media appearances in the lead-up to the vote.
But he admitted there were several areas pro-independence campaigners would need to improve upon on if another constitutional plebiscite was called.
Issues such as “pensions, security of savings and other matters of particular relevance to senior citizens” were those he identified as being weak points in the last campaign, given the large majority of Scots aged 65 and over who voted to reject independence.
There should also be more emphasis on independence “not simply as an end in itself but as a means towards delivering a fairer Scotland that will play a full part in the international community to help build a better world,” he added.
The veteran left-winger sees 2014 as “unfinished business” and remains eager, despite his advanced year, to get involved in a second such campaign.
“I am willing to play as active a part as ever in whatever role I am asked to play,” he said. “There is a special challenge in trying to convert many of my own peer group. I am 76 years young, fighting fit and increasingly optimistic about living in an independent Scotland that will ensure better prospects not just for senior citizens but for future generations.”
Canavan was expelled from Labour in 1999, despite being MP for Falkirk West for 24 years, after announcing his intention to stand in the same constituency at the first elections for the newly created Scottish Parliament.
The left-winger stood as an independent and proved his popularity among the Falkirk electorate by easily beating his official Labour opponent.
He stood down from Westminster in 2000 and held his seat at Holyrood until retiring in 2007.