There are no shortcuts to Scottish independence and it will not happen just because supporters become "more impatient for change", Scotland's First Minister has said.
Nicola Sturgeon said ruling out another referendum indefinitely would be wrong but she indicated that winning a second vote would not happen imminently because the concerns of those who voted No must be addressed "patiently, carefully and comprehensively".
She said she respected the result of last year's historic ballot, which saw Scotland vote to remain part of the UK.
Exactly a year after that poll, she told David Cameron he is "living on borrowed time" as she spoke about the prospect of a second referendum.
While the Prime Minister said it was "time to move on" from last year's ballot, promising action to ensure the Scottish Parliament is a permanent part of the UK's political landscape, Ms Sturgeon told an audience in Edinburgh: "We respect last year's result.
"It would be wrong to propose another referendum without a fundamental change of circumstances or a strong indication that a significant number of those who voted No last year had changed their minds.
"If we are to win independence, we must convince a majority of Scots that it represents the best future for Scotland.
"That was true last year, it is true now and it will be true at all times in the future. There are no shortcuts.
"Independence won't happen just because its supporters become more impatient for change. An even more committed, enthusiastic and impatient 45% is still just 45%.
"If Scotland is to become independent, we must build the support for independence.
"Just as in the referendum campaign, it grew from 30% to 45%, we must in the years ahead take it from 45% to a clear majority.
"That means we must persuade the people we failed to persuade last year.
"That means understanding why they voted No. And it means addressing those concerns, patiently, carefully and comprehensively."
The SNP manifesto for next year's Holyrood elections will set out more detail about the timing and circumstances that could trigger a possible second independence referendum.
Another vote could be sparked if Scotland was removed from the European Union against its wishes in the referendum that is planned before the end of 2017.
Ms Sturgeon said: "I have said before - and I repeat again today - that if Scotland was to find itself facing an EU exit that we hadn't voted for, demand for a second independence referendum could well be unstoppable.
"It would be a material change to the circumstances in which last year's vote was taken."
There has been speculation that the nationalists could also use a vote to renew the Trident nuclear weapons system, the continuation of the Conservatives' "austerity" economics, or failure to fully deliver on the "vow" of more powers for Holyrood, made by the Westminster parties just before last year's vote as triggers for another referendum.
Membership of the SNP has grown from 25,000 a year ago to more than 112,000 today, while two polls this month have suggested that a majority of Scots could now be in favour of leaving the UK.
"My message to David Cameron today is the same as it was when I met him just after the general election," the SNP leader said.
"What happens to support for independence in the months and years to come will depend as much on what you do as it will on what we do.
"And, right now, you are living on borrowed time."
She told Mr Cameron: "If you continue to ignore Scotland's voice, if you continue to disrespect the choice that people across this country made in May, more and more people will conclude that Westminster simply can't deliver for Scotland.
"So, it is your choice, Prime Minister - but know that Scotland is watching."
Mr Cameron said: "''Alex Salmond, Nicola Sturgeon and I signed the Edinburgh Agreement which pledged we would all respect the outcome of last year's momentous vote.
''We all agreed - as do the Scottish public - that the independence referendum should be a 'once-in-a-generation' or a 'once-in-a-lifetime' event. So, now it is time to move on.''
He added: ''Some may want to obsess about separation.
''But I am focused on delivering devolution so that the debate can move on from what powers the Scottish Parliament should have, to how they are used to better the lives of the people of Scotland."
Scottish Labour leader Kezia Dugdale urged the First Minister to stop campaigning for a second referendum and focus on making sure young Scots can have the best start in life.
Ms Dugdale visited a nursery in Aberdeen, which she said was "full of children with a world of possibilities in front of them, a new generation ready to shine".
She said: "The priority of everybody in Scottish politics should be making sure these young people get the best chance in life. That means closing the gap between the richest and the rest in our schools, so that everybody has the skills to make their way in life.
"I want a Scotland where the ability of everybody to get on in life is determined by their potential, work rate and ambition - not by how much money their parents have.
"When we look at the big challenges facing Aberdeen today - a teacher shortage that is fast becoming a crisis and the impact the plummeting oil price has had on jobs and the local economy - it makes no sense for the SNP Government to be focused on campaigning for another referendum.
"Instead of trying to rerun the arguments of the past, we need everybody to focus on creating a better future."
Meanwhile, Scottish Liberal Democrat leader Willie Rennie said "We should be marking the first anniversary of the referendum with a commitment to bring the country together, not creating division with another referendum."
He called on the Scottish Government to "get on with the day job" as he launched a 'to do list' for the First Minister, which included recruiting more GPs, expanding nursery provision and setting up an independent inquiry into Police Scotland
"The SNP should abandon their plans for another referendum so that families and friends don't have to endure that division again," Mr Rennie said.
"The opportunity to focus on the domestic agenda is now before us with the Scottish Parliamentary Elections only a few months away.
"That's why we are launching a to-do list for the First Minister today. The SNP Government need to get on with the day job rather than plotting another referendum."
Scottish Conservative leader Ruth Davidson said: "Before the referendum, Nicola Sturgeon would have told anyone that would listen that this was a once in a generation event.
"She signed the Edinburgh agreement that said that her government as well as the UK government would respect that result. That was quite a clear result. Two million people across Scotland voted to stay within the UK and a year has past from that. Its time to move on."
After the First Minister warned Mr Cameron he was on "borrowed time", the Tory MSP said: "Nicola Sturgeon is trying to ride both horses at the moment, she's trying to reassure the country, but also fire up her membership.
"Today she's been talking about the Union being on borrowed time, but she's also been telling her members that an impatient 45% is still only 45%.
"She seems to think a second referendum is her play thing and she can call it at the point which the SNP can win it. That's her being the First Minister for the SNP and not of Scotland.
"I think business and people in Scotland want to see less wrangling over the constitution, we had a debate, we made a decision, and want to see the Scottish government do its day job and focus on schools, on hospitals on the police force on the economy. That's what we need to see in this country now."