Rishi Sunak's pledge to increase the income tax personal allowance for pensioners is an example of the Tories undoing their own policies, a leading economist has said.

Paul Johnson, director of the Institute for Fiscal Studies (IFS), criticised the plan which would mean OAPs never have to pay income tax on their state pension.

Under the Tory pledge, the personal allowance threshold would be increased for those aged over 66 each year - giving them a tax cut worth around £95 in 2025-26, rising to £275 in 2029-30.

But Mr Johnson said: 'The proposal to 'triple lock' the income tax allowance for pensioners is another example of Conservatives proposing to undo their own tax policies.

'Pensioners used to have a higher tax allowance than working-age people, but since 2010 the tax allowance for pensioners has been cut by more than 10 per cent while that for working age people has risen by 30 per cent.

 Rishi Sunak spoke to employees of a ceramic manufacturing plant, during a Conservative general election campaign event in Stoke-On-Trent yesterday

Paul Johnson, director of the Institute for Fiscal Studies (IFS), criticised the Tory's OAP plan

The tightening of the gap was a shift among over-65s with the Conservatives going from a ten-point lead over Labour to a 20-point lead in the age group

'Going forward, about half of this proposed tax cut is simply not following through with plans for tax rises pencilled in for the next three years.'

Meanwhile, Torsten Bell - chief executive of the Resolution Foundation think-tank which focuses on living standards - said the 'biggest beneficiaries of another tax system complication will largely be better-off pensioner households'.

The Tory proposal would maintain the triple lock, which ensures the state pension increases in line with the highest of either inflation, average wage growth or 2.5 per cent every year.

But the party will also guarantee that pensioners' personal allowances will always be higher than the level of the new state pension.

It comes after a backlash from pensioners following two cuts to National Insurance, which do not benefit them, and being dragged closer towards paying income tax by a combination of rising pensions but frozen thresholds.

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Yesterday, Mr Sunak insisted he had not given up on winning young people's votes after he was quizzed about the contrast between his election offer for pensioners and youngsters.

Along with the pension plan, the PM wants to introduce a new form of national service for 18-year-olds.

But he told reporters: 'I think providing young people - regardless of their background, where they're from, where they live - with the opportunities that national service will provide, the skills that it will give them later in life, will be hugely positive for them.

'And at the same time, foster a culture of service in our country that will make our societies more cohesive, and strengthen our security and resilience as a country.'

Labour said the Tory plan was a 'desperate move' from a party which was 'torching' what was left of its claims to economic credibility.

But a Conservative spokeswoman said last night: 'Labour's Retirement Tax will drag pensioners whose only income is the State Pension into paying tax for this first time.

 'Not only will their tax bill rise significantly, it also means the burden of suddenly being forced to do a self-assessment tax return.

'Be in no doubt, Labour's Retirement Tax will mean millions of pensioners worse off.'