Reforming the triple lock could save £19 billion a year by the mid-2030s, equivalent to almost a thousand pounds for every working household, a think tank has said.

Introduced in 2011, the triple lock guarantees that the state pension will rise every year in line with inflation, average wage growth or 2.5 per cent — whichever is highest.

Pensioners are £1,300 a year better off than they would have been if the state pension had risen in line with inflation over the past decade. But critics say that it has become unaffordable, with the cost rising 70 per cent in real terms in the past 20 years.

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The Intergenerational Foundation, which works to promote economic fairness, is calling for the state pension to increase with inflation until 2030-31 then by the average of inflation and wage growth.

It said that this would save £19 billion a year by 2035, £28.5 billion a year by 2040 and £38 billion a year by 2045.

The triple lock has produced much larger pension increases than were predicted when it was introduced. The foundation said choosing a middle path between inflation and wage growth would reduce these while preserving a link between the state pension and the rising cost of living.

The foundation said some of the savings should be directed to poorer pensioners through a new low-income pension supplement worth £30 a week (£1,560 a year). It suggested that it should be paid to those on pension credit, which tops up pensioners’ income to £238 a week if they are single, or £363.25 if they have a partner.

It said this would cost £1.9 billion a year by 2035 — 10 per cent of the overall savings from the reform.

Conor Nakkan from the foundation said: “The triple lock may have been introduced with good intentions but it has become an expensive and poorly targeted policy. It now delivers large increases to all pensioners, including millions who are already well-off, while younger generations face stagnant living standards, high housing costs and a growing tax burden.”

This year the state pension is expected to cost £146 billion (about 5 per cent of GDP), up from £86 billion in 2005 (when it was 4.14 per cent of GDP). The Tony Blair Institute, another think tank, has estimated that it could rise as high as 7.8 per cent of GDP by 2070 if the triple lock remains.

Tom Selby from the investment platform AJ Bell said that the triple lock has throttled sensible debate about the future of the state pension.

He said there was a danger that the longer the triple lock stays, the more likely it is that state pension age would need to rise further and faster. It already is in the process of rising from 66 to 67 by April 2028, and is set to rise to 68 between 2044 and 2046.

Selby said: “The random nature of how the increase is applied each year also leaves the Treasury exposed to wild fluctuations in the cost of state pension increases each year.”