The future of the triple lock is in doubt as ministers may have to switch to a “more sustainable” way to determine the increase to the state pension.

In the past two years the policy has delivered large increases to payments, with an 8.5 percent rise this past April and a record 10.1 percent hike last year.

But experts are warning such generous increases could soon be a thing of the past. Fiona Peake, pensions expert at Ocean Finance, said of the policy: “It is becoming increasingly expensive.