The Liberal Democrats have pledged to review the case for a single rate of pensions tax relief and committed to maintaining the triple lock in their election manifesto.
The party, which suffered in the 2015 election when it was left with just eight MPs, has also said it will raise all income tax by 1p to raise £6bn for the NHS and social care services and promised its flagship policy of delivering a second EU referendum following the conclusion of Brexit negotiations.
The party said increasing life expectancy is bringing challenges to long-term savings and future pensioners may need an income that can last up to 40 years.
If elected, it would "establish a review to consider the case for, and practical implications of, introducing a single rate of tax relief for pensions, which would be designed to be simpler and fairer and would be set more generously than the current 20% basic rate relief".
Led by Tim Farron (pictured), the party has also promised £100bn of additional infrastructure investment and the legalisation of cannabis, which it claimed would raise £1bn in tax. Its official manifesto launch will take place later on Wednesday.
Institute for Fiscal Studies director Paul Johnson, who on Tuesday suggested Labour was too ambitious in seeking to raise an extra £48bn in tax, told BBC Radio 4's The World at One programme the Lib Dems' numbers add up - although the party itself admitted it is £14bn short and will have to borrow to make up that deficit.
He added: "The costings look like they add up in the sense there are a set of numbers for tax increases they propose, all of which are much more modest than what we saw yesterday [from Labour's manifesto]."
Johnson later told BBC News it was more likely the Lib Dem's 1p across-the-board income tax increase would definitely raise the £6bn they want, as oppose to Labour's proposals to tax high-earners more.
He said: "You can be pretty much absolutely certain the Liberal Democrats would get their money if they did this, and actually Labour wouldn't get that much money. They'd probably only get about £3bn because high earners would change their behaviour."
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