The SNP would demand the power to hold another independence referendum in return for supporting a minority Labour government, the party’s Westminster leader has suggested.
Ian Blackford told the BBC’s Sunday Politics Scotland that the party would not form a coalition with Labour.
But it would be prepared to work with Jeremy Corbyn on a “progressive basis”.
A Scottish Labour source said it would not make “deals, pacts or coalition agreements with any party”.
There have been mixed messages on the issue from Labour in the past. Last month Scottish Labour leader Richard Leonard said the party would commit to opposing a further independence poll in its next UK manifesto.
It came after Mr Corbyn said he would “decide at the time” whether to approve a Section 30 order – the legal power giving Holyrood responsibility to stage a referendum.
As experts predict another hung parliament in the event of a snap election, Mr Blackford was asked whether the SNP’s support for a minority Labour government after a general election would be conditional on support for a Section 30 order.
The MP for Ross, Skye and Lochaber said Labour leader Mr Corbyn had to “respect democracy”.
“We have that mandate there,” he added. “If the people in a Westminster election reinforce that by voting for the SNP, he has to respect that it should be the Scottish Parliament that determines when a referendum is called – not a government in Westminster.”
Interviewer Gordon Brewer asked: “Can I take it that is a ‘yes’?”
And Mr Blackford added: “It is absolutely the case that everything that was seen going on at Westminster demonstrates that the people of Scotland have got to have the right to determine their own future – that means that we have to have that Section 30 sitting in the hands of the Scottish parliament.
In the same interview the MP refused to reveal details of opposition parties’ plans to prevent the UK leaving the EU without a deal on 31 October.
He said they would “seize control of the order paper” if the government does not comply with the Benn Act – which compels the prime minister to request a Brexit delay if no deal is agreed by 19 October.
“The opposition – all opposition parties including the Tory rebels – have a majority to make sure that we can dictate the agenda in parliament any day,” he added.
“So we can bring forward legislation. There are mechanisms that we can put in place. I apologise and you’ll appreciate that I don’t want to go into details on that today but we’ve gamed out all of this and we know exactly how we can do that. “
Boris Johnson has committed to leaving the EU on 31 October, deal or no deal, “but no delay”. But the government has also said it will comply with the Benn law.
Writing in two Sunday papers, the prime minister claimed his latest Brexit proposals have picked up support in Parliament and he urged the EU to compromise.
Mr Blackford called on other parties to bring forward a vote of no confidence in the government as soon as possible – and by the middle of October at the latest.
If that was successful, they would have 14 days to put in place an administration, led by an “caretaker” prime minister.
“We’ve got the Benn Act in place but we’ve still got a prime minister in office that we can’t trust and I’m asking each and everyone one of them to go the extra mile and recognise, whether it’s Jeremy Corbyn or anyone else, what we’re talking about doing is putting someone in No 10 in an administrative capacity to do two things – to send that letter to extend article 50 and to call an election,” Mr Blackford said.
He also addressed the fact that a plan to install Mr Corbyn in Downing Street does not have the support of enough opposition MPs.
“Everyone needs to keep in mind that, whether it’s Jeremy or whether it’s anyone else in that situation, that their hands are very clearly tied by the fact that it’s the collective opposition that are putting that prime minister in place,” he said.
“There’s not a great deal that PM can do unless they’ve got the support of that coalition.”
Meanwhile Christine Jardine, a Scottish Liberal Democrat MP, said her party would not back Mr Corbyn to be interim prime minister.
She said that if Boris Johnson does not comply with the law, “parliament will not allow this country to be crashed out of Europe”.