Labour will fail to win back voters who deserted to the Tories at the last election until it is much clearer about its core identity and driving purpose, according to a new report based on detailed interviews with former supporters.

The analysis by Renaissance, a new group chaired by the frontbencher and MP for Aberavon, Stephen Kinnock, finds that people who had voted Labour previously, but switched to the Conservatives in 2019, will not be convinced to return to the fold by new Labour policies, but instead want big ideas and themes spelling out what the party actually stands for.

Referring to in-depth investigations of the views of its lost voters, said Kinnock: “We found that specific policy proposals did little to break through the cycle of cynicism, because politicians are assumed to break policy promises and they don’t address the fundamental issue of the voter needing to understand Labour’s identity and wider motives before they give the party a hearing.”

The report, while praising Keir Starmer’s recent party conference speech, found that among those ex-Labour backers who had switched to Boris Johnson in 2019, the Conservatives were now seen to have “a record of delivery” on issues such as Brexit, the furlough scheme, vaccinations and running the economy since 2010.

Also, alarmingly for Labour, the interviews showed that the party’s regular criticisms of the Tories for their record on the NHS and for following an austerity agenda were not hitting home with the lost voters. “Traditional attack lines are having little effect,” the report found.

Austerity was seen by many switchers as an unfortunate but necessary economic policy, while higher taxes on the those earning high salaries were viewed as punishing hard work and success.

The report – based on discussions with 60 switchers from different parts of the country, of different ages, backgrounds and views on Brexit – comes amid renewed anxiety in the party over its failure to make inroads into the Conservatives’ lead in the polls, despite the succession of crises that have engulfed the government in recent months. These include continued criticism of its handling of the Covid-19 pandemic, Afghanistan, the cost of living and labour shortages.

In the latest Opinium poll for the Observer today the Tories retain a four-point lead after a party conference season that Labour MPs hoped might see a revival of their party’s and Starmer’s fortunes.

While Johnson’s approval ratings have dropped to their lowest levels since the last election, the Tories are still up two points on a fortnight ago on 41%, while Labour, also up two, lags behind on 37%. The Conservatives and Labour are each holding on to the vast majority of their respective general election voters: 86% of 2019 Conservatives and 85% of 2019 Labour voters.

While voters blame the government for many domestic problems, there is little sign that their frustration is benefiting Labour. The poll found that two-thirds think the government has responded badly to the shortage of HGV drivers and the knock-on effects for the energy market and the economy, while only a quarter (26%) think it has responded well. Even among Tory voters, 42% think the government response has been bad compared with 47% who think it has been good.

Despite this, Starmer remains six points behind Johnson when voters are asked who would make the best prime minister (26% for Starmer and 32% for Johnson). The figures are little changed since August.

Those questioned by Renaissance said Labour needed to be clearer about its central messages if it was to get them back, convince them it was a party of working people and good jobs, that it could manage the public finances sensibly, and that it had a positive story to tell about the future of Britain after Brexit.

Ruth Smeeth, MP for Stoke-on-Trent North from 2015-2019 and a Renaissance advisory board member, said: “Renaissance’s report gives an important insight into how Labour can rebalance the scales reaching out to former voters in Stoke, with a focus on good jobs, security and building a more resilient, proud Britain. If Labour is to rebuild that coalition and to recast itself as a whole nation party of government then it must re-establish itself as the natural party of places like the Potteries.”

The report calls on Keir Starmer to prioritise three of his major conference speech themes – good jobs, value for money, and security. It also calls for Labour to champion a more resilient Britain – building on Rachel Reeves’s “make, sell and buy more in Britain” policy – in order to tell a wider story about how the Conservatives have left businesses, supply chains and critical national infrastructure vulnerable and exposed to hostile capital.