Pensioners have been told they would get a tax break worth £2.4 billion a year as part of a “triple lock plus” plan from the Conservatives.

The Prime Minister will announce on Tuesday that from April next year the income tax personal allowance for pensioners will be increased in line with the triple lock, as he continues the Conservatives’ election campaign.

The pledge would mean both the state pension and pensioners’ tax-free allowance will always rise in line with the highest of earnings, wages or 2.5%.

Billed the “triple lock plus”, the policy is estimated to cost £2.4 billion a year by 2029/30, a price tag which mirrors Mr Sunak’s proposed national service duty for all 18-year-olds, billed at £2.5 billion a year.

For individual pensioners, it would be worth around £100 in 2025 according to the Tories, and would grow over time, adding to their incomes on top of rises in the state pension.

The tax cut will be funded through a previously announced plan to raise £6 billion a year by the end of the next parliament by clamping down on tax avoidance and evasion.

The Prime Minister said: “I passionately believe that those who have worked hard all their lives should have peace of mind and security in retirement.

“Thanks to the Conservatives’ triple lock, pensions have risen by £900 this year and now we will cut their taxes by around £100 next year.”

The policy follows criticism of Chancellor Jeremy Hunt’s decision to cut national insurance by 2p at the spring budget, after a similar cut in the autumn.

State pensioners did not benefit from the cut, as they do not pay national insurance.

Labour claimed the Tories’ offer to pensioners was not credible.

“Why would anyone believe the Tories and Rishi Sunak on tax after they left the country with the highest tax burden in 70 years?” said Jonathan Ashworth, the shadow paymaster general.

He added: “This is just another desperate move from a chaotic Tory Party torching any remaining facade of its claims to economic credibility.

“Not only have they promised to spend tens of billions of pounds since this campaign began, they also have a completely unfunded £46 billion policy to scrap national insurance that threatens the very basis of the state pension.

“Labour will protect the triple lock. But Rishi Sunak is planning to reward Britain’s pensioners for their loyalty by stabbing them in the back, just like he did to Boris Johnson and just like he has done to his own MPs.”