The SNP is launching its general election manifesto, which calls for an independence referendum “at the end of the Brexit process”.
The UK government has already rejected Nicola Sturgeon’s call for a vote to be held in the autumn of next year or spring of 2019.
But the SNP says that position will be “democratically unsustainable” if it wins a majority of Scottish seats.
The manifesto also sets out plans to invest £118bn in UK public services.
The party also pledges to increase the minimum wage, and wants Scotland to have control over immigration and to remain in the EU single market after Brexit.
But much of the focus will be on what the manifesto says about a second independence referendum.
Prime Minister Theresa May repeatedly saying that “now is not the time” for a second referendum.
And the Conservative manifesto promises there will be no referendum until the Brexit process has “played out” and unless there is “public consent” for one to be held – although it does not specify what that means.
Speaking ahead of launching her party’s manifesto, Ms Sturgeon said the SNP would “always make the case that Scotland should have the right to make our own decisions on Scotland’s future – and stand against any Tory attempts to diminish the powers of our Scottish Parliament or reverse the gains of devolution”.
She added: “Only the SNP can provide the strong opposition that Scotland needs to protect our schools, hospitals and vital public services from deeper Tory cuts and further damaging austerity.
“And if the SNP win this election in Scotland, it will strengthen the country’s hand when it comes to opposing cuts, defending our place in Europe and on choosing our future as a nation.”
Labour leader Jeremy Corbyn has also firmly opposed a second referendum in recent weeks, claiming it is “unnecessary and unwanted”, despite saying earlier this year he would be “fine” with one being held if the Scottish Parliament called for it.
However, in a radio interview on Monday, Mr Corbyn said he would “open discussions” with the Scottish government if he becomes prime minister – but said he would suggest they “think very carefully about it”.
The SNP won an unprecedented 56 of the 59 seats in Scotland at the last election – and is widely expected to remain as comfortably the largest party this time around despite opinion polls suggesting it is likely to lose some seats.
Ms Sturgeon, who is Scotland’s first minister, argues that she already has a mandate to hold a referendum after winning the last Holyrood election on a manifesto that stated there should be another vote on independence if Scotland was taken out of the EU against its will.
‘Strengthen the case’
The Scottish Parliament formally backed Ms Sturgeon’s call in March, with the combined votes of SNP and Scottish Green MSPs being enough to defeat the pro-UK Conservatives, Labour and Liberal Democrats.
Ms Sturgeon told the BBC’s Andrew Neil in an interview on Sunday that the election would “not decide whether or not Scotland becomes independent”.
But she argued that another victory for her party in Scotland would strengthen the case for a referendum.
She said: “I want Scotland to have a choice not now but at the end of the Brexit process when the options are clear.”
The SNP had originally been scheduled to unveil its manifesto last week, but the event was postponed following the Manchester terror attack.
It will set out an “alternative to Tory cuts” that the party says would see an additional £118bn invested in public services.
The SNP will seek to protect the triple lock on pensions, stop cuts to the winter fuel allowance and deliver extra investment for the NHS, for social security and other vital public services.
And it will promise to increase the minimum wage as part of a plan to improve living standards and tackle inequality.
It would seek to fund its spending plans by delaying reducing the deficit and increasing tax revenues by raising income tax to a new 50p rate across the UK.
The manifesto will also call for Scotland to have control over its own immigration policy.
Ms Sturgeon has sought to portray the election as a chance to protect Scotland from Conservative policies, arguing that Scottish votes for the SNP “can stop Theresa May having a free hand at Westminster to do whatever she wants”.
She has also said she would be open to seeking a “progressive alliance” at Westminster to keep the Conservatives out of government in the event of a hung parliament.
But she has predicted that the Conservatives will win another majority in the election – and has said Mr Corbyn is not a credible candidate to be prime minister.
Mr Corbyn has insisted he would not do a deal with the SNP to gain power at Westminster, pledging: “There will be no deals. There will be no alliance. We’re fighting this election to win.”
Meanwhile, the Scottish Conservatives are to publish fresh plans to improve standards in Scotland’s schools as part of its demand for Ms Sturgeon to focus on “education, not separation”.
Scottish Conservative leader Ruth Davidson said: “Nicola Sturgeon asked to be judged on education. Standards are down, there is a teacher shortage, we have a curriculum in crisis and our poorest children are being let down.”
The Liberal Democrats have also attacked the SNP over its record in government in Scotland, arguing that the party has “taken its eye off the ball” on health and education while it pursues an independence referendum.
Scottish Lib Dem leader Willie Rennie said: “The SNP manifesto needs to cancel the divisive independence referendum so that the SNP can finally turn their attention full time to Scottish public services.”