More than twice as many people trust Theresa May and Philip Hammond to run the economy than Jeremy Corbyn and John McDonnell, according to a new poll on the eve of the autumn statement.

Just 18% of voters would trust the Labour leadership to manage the public finances, the findings of the Opinium/Observer poll show, compared with 44% who have faith in the prime minister and chancellor.

The Conservatives’ lead comes despite claims that May’s government has no clear plan for Brexit and as business leaders and politicians across the political spectrum put pressure on the government to define its strategy.

May’s positive approval rating is down just one point since last month, with 43% backing her performance as prime minister and 25% disapproving. By contrast, 17% of voters believe Corbyn would make the best prime minister, compared with 45% for May.

Labour’s overall poll rating is down three points from last month at 29%, while the Conservatives are up one point at 41%. Ukip are on 12%, the Liberal Democrats on 7%, the Scottish National party on 6% and the Greens on 4%.

The chancellor’s autumn statement will be a key test for May’s government as it moves to deliver on its promise to prioritise those families who are “just about managing”. In a sign that the prime minister’s messaging on the issue is resonating with voters, 43% of those who told Opinium they were “coping” financially said they most trust the prime minister and chancellor on the economy, compared with just 17% for Corbyn and McDonnell.

However, Hammond is likely to deliver a grim set of projections in the Commons next week, as the Office for Budget Responsibility releases its first assessment of the impact of Brexit on growth.

Whitehall insiders say that on Wednesday, the chancellor will offer modest but popular giveaways to such families, who typically have a net household income of between £12,000 and £34,000.

An increase in the tax-free personal allowance to more than £11,000, a move backed by 48% of the public, will likely be among them. Nearly two-thirds (64%) of those with a net household income between £20,001 to £25,000 a year believe such an increase would improve their financial situation, as did 52% of those with a yearly income of between £15,001 and £20,000.

Other popular policies include a cut in the basic rate of income tax, backed by 30% of voters, and an end to the public sector pay freeze, backed by 21%. Reports suggest Hammond is considering freezing fuel duty for motorists, increasing support for childcare and helping low-income families to save.