AN SNP election win will seal a “triple lock” on a second independence referendum, Nicola Sturgeon has said, while admitting her proposed timetable could slip beyond spring 2019.

Launching her party’s manifesto in Perth, the First Minister said she had already secured a mandate based on Brexit, and this had been reinforced by a recent vote in Holyrood.

But if SNP MPs were elected in most of Scotland’s 59 seats, it would make it “democratically unsustainable" for Theresa May to deny Scots a vote on their future after the Brexit process.

The manifesto said such a win would “complete a triple lock” on a referendum.

The Unionist parties said the First Minister was prepared to jeopardise jobs and the economy, regardless of cost, in a headlong pursuit of independence.

Ms Sturgeon announced in mid-March that she wanted a vote "between the autumn of 2018 and the spring of 2019", once Brexit terms were known, to give Scots a choice between a hard Brexit in the UK and pro-European independence.

When MSPs voted 69-59 in favour of Holyrood having referendum powers, they did so on a government motion which mentioned the same dates.

However there was no timetable in the manifesto yesterday, prompting speculation the SNP leader was sidelining her plan after Mrs May insisted “now is not the time” for a new vote.

The recent Tory manifesto also said there could be no vote without demonstrable “public consent” after the Brexit process had “played out” for an undefined period.

Ms Sturgeon said: “I said autumn 2018 to spring 2019 for a reason, because that is when Theresa May is saying the Brexit process will end. So I’ve taken her at her word.

“If that changes - I said this on the day I set out these plans - if that changes, then of course we will have to consider our timing in light of that.

“The key point of principle for me is clarity at the end of a process to allow people to make a genuinely informed choice about the future of our country.”

Sources close to the First Minister later insisted there was no shift in policy or any desire to kick the referendum into the long grass.

For just the second time in 20 years of Westminster and Holyrood elections, the SNP leader did not appear on the manifesto cover, which featured pictures of babies and young children.

Ms Sturgeon denied she was becoming a more divisive figure on the doorstep, adding: “The baby is much cuter than me.”

In other election developments:

* Jeremy Corbyn was unable to give the cost of his free nursery care policy on Radio 4’s Woman’s Hour and was upbraided for trying to check the figure on his iPad

* Mr Corbyn refused to say if he would block an independence referendum if MSPs wanted it

* Mrs May said the Labour leader would find himself “naked and alone” in Brexit talks

* The Evening Standard, edited by former Chancellor George Osborne, said the Tory campaign had suffered “the most disastrous manifesto launch in recent history”

* The SNP was accused of a “misusing” the NHS logo by altering it to read NHSNP

Addressing SNP activists at a packed Perth Concert Hall, Ms Sturgeon said there was “too much at stake for Brexit simply to be imposed on Scotland, no matter how damaging".

She said: "Our future must be decided by us, not for us.

"Any continued Tory attempts to block Scotland having a choice, when the time is right and the options are clear, would be democratically unsustainable."

However she twice failed to explain how, in practice, she could overcome resistance by a determined Mrs May.

Scottish Tory leader Ruth Davidson said "nobody is fooled any more" by Ms Sturgeon: “Strip away the bluster and it’s written down in black and white - she wants to drag Scotland back to another referendum by as early as next autumn.

“That would cost jobs, risk our economy, and distract us all from the real job in hand - improving our schools and public services.

“This was a tired launch by a First Minister who has failed to give people a reason for voting for her party.”

Scottish Labour leader Kezia Dugdale said Ms Sturgeon had confirmed her “number one priority” in the election was “another unwanted and divisive independence referendum”.

Scottish LibDem leader Willie Rennie added: “The SNP must think we are stupid. They barely mentioned independence but we know independence will be their top priority once the election is over.”

Mr Corbyn will today try to shift the debate away from Brexit to public services, saying the NHS and schools “are at stake in this election” after being starved by the Tories.

Meanwhile Ms Sturgeon, whose 2015 success was partly down to Labour voters backing the SNP, will try to stop the tide flowing back to Labour by warning a vote for Mr Corbyn’s party risks "letting Tory MPs in by the backdoor”.