Jeremy Corbyn and Jo Swinson must “step out of the sand pit” and back the SNP’s vote of no confidence in the prime minister, the party’s Westminster leader Ian Blackford has said.

Accusing Labour of “running scared” from a general election, Blackford opened the SNP’s conference in Aberdeen with the challenge to other opposition leaders to “step up to the job” as his party’s leader, Nicola Sturgeon, piled pressure on Corbyn over a second independence referendum

Earlier in the day, Sturgeon warned the Labour leader that he should not “bother picking up the phone” seeking her support to form a coalition government, unless he was willing to grant another referendum.

Blackford told delegates: “Let’s come together – back a vote of no confidence – get rid of Boris Johnson, secure that extension and give power back to the people with a general election. Jeremy, Jo, the clock is ticking. The SNP is ready to act. Are you?”

Contrasting Westminster’s “dysfunctional, dangerous” government with the SNP’s administration at Holyrood, Blackford praised Sturgeon’s “outstanding leadership” of the party and in her role as first minister.

Blackford dismissed the Queen’s speech, to be held on Monday, as “simple electioneering,” adding that SNP MPs were ready to vote it down, and urging Labour and Liberal Democrats to do likewise.

While commending the work of his SNP colleague Joanna Cherry and others challenging Johnson’s government through the courts, he added that “this perpetual cycle of court cases and parliamentary defeats – while it is effective – is no way to run a country”.

He said: “We should not have to rely on the courts to solve our problems, or on arcane Westminster procedures to find ways to block the government. We should not be tolerating this Tory government in office at all.”

Blackford was also applauded by delegates as he cautioned them that only a legally-constituted independence referendum would be accepted by voters and by EU member states. “Plan Bs are by definition second best,” Blackford said.

Immediately after Blackford’s warnings, moves by a small group of rebels who believe the SNP should keep the option of demanding independence without a legally-constituted referendum were heavily defeated by the party leadership.

Chris McEleny, an SNP councillor in Inverclyde, said the party needed to have that so-called “plan B” option in reserve since Boris Johnson was expected to reject Sturgeon’s calls for a section 30 order authorising a referendum. He said that if Scotland voted for a majority of pro-independence MPs at the next election, that should be enough to trigger talks with the Westminster government.

McEleny’s measure is backed privately by a number of SNP parliamentarians close to Alex Salmond, the former party leader, including Angus MacNeil, the SNP MP for the Western Isles. The conference overwhelmingly defeated the proposal.

Earlier on Sunday, Sturgeon said that any Westminster leader seeking SNP support should “not bother picking up the phone” if they were not prepared to grant Holyrood the legal powers to hold a second independence referendum.

On Saturday, shadow chancellor, John McDonnell, insisted that there would be “no pacts, no deals, no understanding” with the SNP for supporting a Labour-led national unity government. McDonnell stunned colleagues in August and contradicted party policy when he suggested at an Edinburgh festival fringe event that Labour should allow Holyrood to stage a second independence referendum if MSPs vote for one.

Sturgeon told BBC One’s The Andrew Marr Show: “I don’t favour coalitions. We would favour a progressive-type alliance. But I would say this to Jeremy Corbyn, or any Westminster leader who is looking to the SNP for support, if you don’t accept Scotland’s right to choose at our choosing – don’t even bother picking up the phone to me.”

Speaking as a Panelbase poll for the Sunday Times showed that support for independence had risen to 50%, she added that she will request another independence referendum from the prime minister in “a matter of weeks”.