The three main political parties are not being honest with voters about the spending cuts and tax rises needed after the general election, a think tank has warned.

IPPR analysed the promises made by the Conservatives, Labour and the Liberal Democrats at their recent annual conferences, and found they lacked the detail necessary to allow the public to make an informed choice next May.

Spencer Thompson, senior economic analyst at IPPR, said: “With all three parties committed to a course of deficit reduction in the next parliament, it is surely incumbent on them to let us know where they are planning to cut spending and what taxes they intend to increase. Between now and the election they need to spell out in much more detail their plans.”

The study found that the Conservatives would hit the bottom 10 per cent of the income ladder hardest if they retain power, after promising a two-year freeze on most working age benefits from 2016.

According to the IPPR, the Tories’ plans would have “a significant impact on the poorest families, as tax credits and benefits make up a larger share of those families’ incomes.”

This group would not gain from the £7.2bn of tax cuts pledged by David Cameron, while those at the top would benefit. The report says the “unfunded” Tory tax cuts would probably mean deeper spending cuts rather than other tax increases.

Conversely, Labour’s plans, including a mansion tax on homes worth more than £2m and raising the top rate of income tax from 45p to 50p, would squeeze the top 10 per cent on the income scale.

The IPPR says that Labour has outlined only “a very small proportion” of the cuts needed to eliminate the deficit by 2020. Although the party promised £400m of savings by limiting child benefit rises to one per cent for the first two financial years, the study suggests it would raise only £100m because the Coalition already plans to cap the increase at one per cent in the first year. It describes as “highly uncertain” the likely revenue from Labour’s planned 50p top rate and tax on bankers’ bonuses.