Less than a quarter of Scots are in favour of breaking away from UK, according to survey

Support for independence among Scottish voters has slumped to its lowest level since devolution, with less than a quarter now in favour of breaking away from the UK, according to a Scottish Social Attitudes study. It found only 23% of voters support independence, nine percentage points down on last year, with voters less optimistic about an independent Scotland's chances of tackling poverty and improving its economy.

The findings are a significant setback for Alex Salmond and the pro-independence Yes Scotland campaign as they prepare to intensify their efforts to persuade voters before next year's referendum. The survey found support for staying in the UK now stands at 72% – the highest yet.

The annual study, based on detailed face-to-face interviews with voters, suggests Salmond's success as first minister in championing Scotland's cause within the UK has weakened overall backing for independence. Since he came to power in 2007, backing for independence in its polling has averaged 26%, compared with 30% before he took office. The lowest levels of support for independence in this survey have come during his time in office: it hit 23% in 2010 and again last year.

The study found that support for greater powers for the Scottish parliament within the UK, including control over welfare and taxation, appears to have grown as the most popular option. It said 56% wanted to run taxation and 64% the welfare system. Two-thirds want Holyrood to control nearly all Scotland's affairs.

Those findings will intensify pressure on Scottish Labour, as the main opposition party, to produce detailed plans for greater devolution as an alternative to independence, well before the 2014 referendum.

Neither Salmond nor his deputy, Nicola Sturgeon, responded to the findings but their officials highlighted the pro-devolution figures on welfare and taxation, citing them as proof that confidence in Holyrood's role was increasing.

Signalling a switch in emphasis towards promoting greater devolution as a possible consolation prize and targeting voters who support stronger devolution, Salmond's spokesman said: "There are negatives but there are positives as well in terms of the proportion who say they would support the Scottish parliament having responsibility for things like welfare and taxation."

Ignoring the Scottish Liberal Democrat proposal for Holyrood to control welfare and large areas of taxation, he added: "An independent Scotland is the only option on the table that meets that aspiration. What we can categorically say is that all these powers and responsibilities are on offer to the people of Scotland if they vote yes in next year's referendum."

He said the benefits and gains from independence would become much clearer to voters as the Scottish government's proposals were unveiled during 2013, ending in publication of its full "prospectus" for independence this November.

Blair Jenkins, chief executive of Yes Scotland, admitted the campaign had "hard work" to do to win the independence referendum, but said the survey was already out of date. It did not take account of the impact of welfare reform or David Cameron's referendum on Europe.

"Since the poll was conducted from July to November last year, we have had the Westminster welfare changes, making one million Scots families worse off, and the UK government threatening to take us out of Europe, our largest trading market," Jenkins said.

John Curtice, the lead author of the Scottish Centre for Social Research study, which interviewed 1,229 people, said that before devolution hardline supporters of independence had highlighted the paradox now faced by Salmond.

For hardliners, "this was always a trap of devolution: it's success would help the system. While Salmond's effectiveness has given them this unparalleled opportunity to hold the referendum, there's this paradoxical backdrop that grievance about the union has become less. That has made the referendum rather more difficult to win."

Johann Lamont, the Scottish Labour leader, said Salmond's referendum was a "vanity project" which was, like David Cameron's referendum on Europe, damaging the economy. "The SNP and the Tory Party now share the same destructive agenda. They both want referendums which, as Nicola Sturgeon has admitted, cause uncertainty and cost jobs at a time of economic crisis," she said.