The state pension is set to rise to over £13,000 a year from April, based on the latest wage growth figures. The full flat-rate pension will increase by £488, taking the annual payment to £13,036.40. The basic state pension for those who reached pension age before 2016 will rise by £374.40 to £9,989.20.

The increase is determined by the triple lock policy, which guarantees the state pension rises by the highest of average earnings growth, inflation, or 2.5%. Average earnings, including bonuses, grew by 3.9% in the three months to July, according to the Office for National Statistics. This figure is expected to drive the pension uprating.

The flat-rate pension will exceed the £12,570 personal allowance, meaning some pensioners with no other income will become liable for income tax. Around 13 million people receive the state pension across the UK.

Ruth Curtice, chief executive of the Resolution Foundation think tank, said the triple lock creates a ratchet effect where pensioners' living standards grow faster than typical workers. She said pensioners have seen living standards grow three times more than typical workers over the last 20 years.

Jonathan Cribb, deputy director of the Institute for Fiscal Studies, said each increase in spending builds upon the last, making the long-run cost substantial but uncertain. State pension spending is already at £154 billion this year, with forecasts suggesting it could rise by a further £600 million a year by 2029-30.

Pensioner groups say many older people still face cost of living pressures such as high energy bills. The state pension remains small compared with state provision in Europe.

The Labour government has previously promised that pensioners who rely solely on the state pension would not be required to complete a tax return. Asked on Tuesday whether that commitment still stands, Business Secretary Jonathan Reynolds said any changes to personal allowances and tax rates would be set out in the Budget on October 28.

Analysis by consultants LCP suggests only one in 16 pensioners would benefit if the government kept to its previous pledge, saving about £91 each a year. Sir Steve Webb, a partner at LCP and former pensions minister, said the government's plans on this point are a mess.

The triple lock policy has been defended by Labour until 2029, but economists have warned about its cost ahead of the Budget. The state pension age is rising to 67, but government spending on pensions continues to climb.