Rishi Sunak will guarantee that the pensions triple lock will remain in place under a future Conservative government, Sky News understands.

The costly policy came under fresh scrutiny after Chancellor Jeremy Hunt warned this week that improved economic growth and public sector spending cuts might be needed to sustain it.

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However, a Treasury source said the Tories – which introduced the triple lock in 2010 – will stick with it when the nation goes to the polls.

The triple lock is a government promise to raise state pensions every year by the level of average earnings, inflation or 2.5% – whichever is the highest.

It was designed to ensure people’s pensions are not impacted by gradual rises in the cost of living over time – but an ageing population and soaring inflation has raised questions about its long-term affordability.

A recent report by the Institute for Fiscal Studies (IFS) said the triple lock added an extra £11bn a year to public spending.

Asked about the sustainability of the triple lock and the pension age, Mr Hunt told the Lords Economic Affairs Committee on Tuesday that both of those things are “kept under review”.

He added: “The answer is very contingent on how successful we are.

“If we are able to run public services more efficiently, if we are able to increase our long-term growth rate, then it is entirely possible we can continue to have the levels of public provision we currently have, and the support for pensioners, and I very much hope that is the case.

“We are confident we can continue to support pensioners in the way we have been in the past.”

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The comments sparked concern that the future of the triple lock was under threat.

But speaking to the Express, which first reported on plans to keep the policy, Mr Hunt said: “I am totally committed to the triple lock, which is increasing the state pension by 8.5% next month – worth £900. Our track record is clear: we stand square behind Britain’s pensioners.”

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The general election, expected in the second half of this year, will be heavily fought on the economy.

Both the chancellor and his Labour counterpart Rachel Reeves have set out strict fiscal rules on public spending.

It has been reported that Labour will also commit to the triple lock in its election manifesto.

Any backtrack on the policy would be politically risky, given the UK’s state pension provision is lower than most other advanced economies and warnings about rising pensioner poverty.

However, critics say that on top of its unsustainable cost, it contributes to inter-generational unfairness.