The SNP Westminster leader will today make a speech suggesting denying Scotland a second independence vote is only driving support for another referendum.
Speaking at the Institute for Government's inaugural annual conference, he will appeal to the Westminster parties to "free themselves from the dead end of denying democracy".
Making his first speech as leader, he is expected to say: "At the Scottish Parliament election, a record majority of MSPs were elected on a mandate to hold an independence referendum.
"In a functioning democracy, the UK Government would have accepted that democratic vote by the people of Scotland and agreed to a referendum. Instead, Westminster has turned the UK constitutional debate into a full blown crisis of democracy.
"Following the Supreme Court judgement, the SNP took the conscious decision to reflect on the next steps to deliver the democratic choice that people in Scotland have consistently voted for.
"In stark contrast, Westminster has failed to reflect, refused to engage and won't countenance respecting the democratic rights of people in Scotland. Having campaigned for 'No' in 2014, it appears the word 'No' is literally all the Westminster parties have left.
"But a 'just say No to democracy' strategy is doomed to fail. Not only is it driving up support for independence, but it's fatally undermining any remaining case for Westminster control.
"No one is asking Westminster to say 'Yes' to independence, but moderate unionists know they need to release themselves from the dead end of denying democracy – or they will do more to make the case for independence than any Scottish Government could ever do."
It comes with the party set to hold a special democracy conference in March to decide the way forward to secure independence, after the UK Supreme Court ruled in November the Scottish Parliament does not have the power to hold another vote on the issue.
Following the Supreme Court ruling, First Minister Nicola Sturgeon said the SNP would fight the next general election as a de-facto referendum. The SNP’s National Executive Committee has also set out an alternative option of contesting the next Scottish Parliament election in 2026 on that basis.