Alex Salmond has attacked the campaign against Scottish independence as "the most miserable, negative and depressing" political movement in modern history, as he rallied his party in preparation for September's referendum.

The Scottish National party leader told his party's spring conference, which also marked the party's 80th birthday, that the negativity and a loss of faith in Westminster were driving hundreds of thousands of voters who were not nationalists to support a yes vote.

"The more the people of Scotland hear the case for no, the more likely they are to vote yes," Salmond told more than 1,000 SNP activists in Aberdeen. "They are already out of touch with the people and are now losing touch with reality."

Salmond cited "poverty-creating policies" from Westminster, the "utterly ludicrous" claims by former Nato secretary general Lord Robertson last week about the threat posed by independence to global security, and the Labour party's alliance with the Tories in the no campaign. Despite the repeated warnings from David Cameron's government about the risks of a yes vote to Scotland's economy, Salmond said the referendum was a model of modern democracy.

"A people exercising their right to self-determination in a lawful, agreed, respectful, democratic manner is a not a threat but a noble thing," he said, rousing the crowd of activists to roars of support with a speech heavy on rhetoric but short on policy.

"The yes campaign is positive, uplifting, hopeful and must always stay that way," he added, concluding: "This is our moment. To be a beacon of hope. A land of achievement. Our country, our Scotland and our independence."

Despite evidence that the negativity of the no campaign has seen a steady increase in support for independence, with five months to go to the referendum on 18 September, the yes campaign still lags in the opinion polls. SNP strategists say their full independence campaign will not start until late May.

Recent opinion polls show that, excluding don't knows, the yes vote is now as high as 46%, but including all voters, it is still under 40%. The SNP is now making an explicit appeal to Labour voters and undecided women voters, who are less likely to back independence than men.

He claimed the independence cause did not belong to him or to the SNP, and said Scottish Labour supporters could use it to revitalise their party, free of Westminster control. If voters did back independence, he said, he would appoint a cross-party Team Scotland to represent Scotland in negotiations.

Now in his eighth year as first minister, having first won power in 2007, Salmond announced the promotions of two junior women ministers to full posts in the Scottish cabinet, on full cabinet salaries, in an attempt to contrast his government with Cameron's government, which has been criticised for its failure to promote women.

Salmond promoted Shona Robison, the sports and equalities minister – who has been under attack for her role in the decision to blow up the Red Road high-rise flats in Glasgow for the Commonwealth Games opening ceremony – and Angela Constance, the minister for youth employment.

That, he said, would take female membership of his cabinet to 40%, simply by increasing the number of full cabinet ministers from eight to 10. Neither of these new posts will include extra junior ministerial posts, however. "There is no overall increase in ministers," Salmond's spokesman said, risking charges of tokenism.

Salmond then stressed the Scottish government's £250m plans to expand childcare provision and enforce the equal pay act. On Friday, in one of the few policy announcements at the conference, Nicola Sturgeon, the deputy first minister, said her government had found £1m extra to support food banks and £5m a year to reinstate the independent living allowance for disabled people which had been scrapped by Maria Miller, the former UK minister for disabled people who resigned as culture secretary last week.