New Conservative leader Theresa May has been described as the most right-wing prime minister since Margaret Thatcher by the SNP's Angus Robertson.
Pushing for renewed independence, Robertson formally launched his bid to become depute leader of the SNP with a warning to May that her days as leader of the whole of the UK will be numbered if she fails to respect Scotland's desire to remain part of the European Union.
Almost two thirds (62%) of voters north of the border backed keeping the UK in the EU in last month's referendum, with SNP leader and First Minister Nicola Sturgeon saying afterwards that the result makes another vote on Scottish independence "highly likely".
Robertson, the SNP leader at Westminster, hit out at May after she said on a visit to Edinburgh that Scots have "had their vote" on independence in 2014 - making it clear the opinions of Scottish people would not be stifled by hers.
In a speech, Robertson told an audience in the Scottish capital on Thursday evening: "Just last week, Theresa May said that options for keeping Scotland in the EU were 'impractical', and that we've 'had our referendum'. I think we have an opportunity to show her that things are different in Scotland.
"She has of course said that there will only be a 'UK approach' to Brexit. She has refused to accept that for Scotland, Remain means Remain.
"My message to the Prime Minister is this: If you ignore the expressed will of the people of Scotland, if you refuse to even consider how we might protect Scotland's place in the EU then be in no doubt - your days as Prime Minister of a United Kingdom are numbered."
Robertson added that the next few months will be a "major test" for the SNP - which now has more than 120,000 members - with the party facing the prospect of "delivering a new prospectus for independence".
He told SNP members and activists: "Our next job is to communicate with the many people who believe their 2014 referendum vote was to stay in Europe by voting 'no' to Scottish Independence. They are right to feel cheated. They are right to feel betrayed.
The MP, who joined the SNP as a teenager in the 1980s, said he has the necessary skills and track record to be depute leader, outlining leadership, engaging grassroots members across Scotland, and independence as the three themes to his campaign.