Concerns have been raised in Parliament about the future of the triple lock. Experts told the Work and Pensions Committee that the policy could soon become unaffordable. But they also warned it's hard to know what should replace the policy as the purpose of the state pension is "not clear".

The comments came in a committee meeting looking at the future of the state pension age. The state pension age is currently 66 for both men and women, but this is gradually increasing to 67, between April 2026 and April 2028. Lifting the access age for the benefit is one way for the Government to curb the ever-rising state pension bill.

Another way they could slash the rising welfare bill thanks to the state pension is to change the triple lock. This policy guarantees that state pension payments increase in line with whichever is highest of 2.5 percent, the rise in average earnings or inflation.

Appearing before the committee were Jonathan Cribb, deputy director of the Institute for Fiscal Studies, and Chris Curry, director of the Pensions Policy Institute. Liberal Democrat MP John Milne asked the duo for their thoughts on "what kind of test or principle" should be applied to decide when the triple lock will need to change, as the policy "looks to be very expensive".

The triple lock has delivered big increases in recent years, including a record 10.1 percent pay boost in April 2023, thanks to high levels of inflation. Payments are set to rise 4.8 percent next April, lifting the full new state pension from the current £230.25 a week to £241.30 a week.

Mr Curry said: "It's very difficult to see if there's a particular test you could use. It has been very successful in increasing the overall level of the state pension, it has had a big impact in reducing pensioner poverty, although some of that might be undone by changes in housing coming forward."

"I think it's very hard to see how the triple lock will be ended without it being part of a broader review or set of changes. I think one of the real challenges we have it's not really about the triple lock it's about the state pension.

"It's not entirely clear what the purpose of the state pension really is, what is the policy objective of the state pension. Without knowing what that is, it's very hard to determine when you've reached that objective or how you then maintain that objective."

However, Mr Curry said there is one project underway that should consider the triple lock. He said: "I think it's something that the Pensions Commission should be looking at, I think it's something you need to look at alongside the state pension age.

"You'd probably need to consider the age, the overall level of pension and the indexation together, and work out what you think is the right combination of those things, to meet the purpose that you think the state pension is for."

The Pensions Commission is set to look at the questions of the adequacy, fairness and sustainability of pensions provision, and will make recommendations to the Government.

Mr Cribb said: "Most people agree that the triple lock mechanism is ultimately unsustainable and ultimately a more sustainable mechanism that doesn't ratchet it up constantly will need to be found."

Suggesting how the policy could be changed, he said: "You could try to move away from the triple lock while providing some additional support for people in the private rented sector. Their housing benefit is not particularly generous."

He spoke about another group who could be given extra support: "There are a set of much older people, such as women who reached state pension age before 2010 have a massively less generous state pension on average. Trying to address some other inequalities in the system, which you could do if you moved away from the triple lock, because you'd have the Exchequer gain from moving away from the triple lock."

The state pension age for women increased gradually from 60 to 65 from 2010, to bring it in line with men. This was part of changes to create a single state pension system for both men and women.

Under the old system, women had a lower state pension age but often received a lower state pension than men, as they may have taken several years out of work to care for children and so would have lower National Insurance contributions.

Married women also previously had the choice to pay a reduced rate of contributions, under the married women's stamp policy, meaning they built a lower entitlement and would instead claim a pension based on their husband's contributions.