Lord Turner, the architect of radical reforms in which the retirement age will rise to 68 by 2046, has told The Times of London that with no limit in sight for life expectancy, people are going to have to work even longer than he proposed.

In an interview with the British newspaper marking the 100th anniversary of the state pension today, Lord Turner predicted that a future government would have to reopen the question of raising the state pension age soon after it reaches 68.

'This is not the end of the story. If the value of the pension is to be protected, the retirement age will have to rise again. I would be amazed if, around 2055, the government of the day were not taking the retirement age higher and we'll be at 70 by the end of the century,' he told the newspaper.

In 2005, the Pensions Commission headed by Lord Turner called for pensions to be payable at a later age over the coming decades as life expectancy rises. His recommendation to raise the retirement age to 68 was adopted by the government in 2006.

The government will gradually increase the retirement age from 65 to 66 in 2024, to 67 in 2034 and to 68 by 2046.

The changes proposed by Lord Turner were the biggest overhaul of Britain's pension system since modern welfare benefits were created in 1946.

Ministers had earlier also adopted his proposal to set up a low-cost national private savings scheme to which employers must contribute, although they have the right to opt out if they do not want to be members.

However, Lord Turner's latest suggestion that the retirement age should keep rising has attracted angry criticism from campaigners.

'After a period of working for 40 or 45 years, society should endow on people a period of retirement of not just two or three years,' said Mr Neil Duncan-Jordan, spokesman for the National Pensioners Campaign.

'If the retirement age is raised to 70 for some groups of people, especially low-paid manual workers, life expectancy is not much beyond 70 or 75. Five years is not exactly the 'lifetime in retirement' people have been promised,' he said.

Mr Mervyn Kohler, head of public affairs at Help the Aged, said that ministers needed to show flexibility.

'I entirely buy the principle that links the state pension age with life expectancy, so people spend roughly the same amount of time working and in retirement. But I do not believe they should be set in concrete...

'If some experts are correct, growing rates of obesity and other health problems could lead to declining life expectancy, so the pension age should actually come down in those circumstances,' he argued.

Mr Chris Grayling, Conservative pensions spokesman, did not oppose Lord Turner's view. 'More and more governments are going to see retirement as a process and not a single date. Consequently, a single retirement age won't be as much of the future as of the past,' he said in a Times report.

In Singapore, the Government is encouraging more older people to continue working so that they have enough savings for their golden years, as people are living longer.

A new law, which requires companies to re-employ older workers, is targeted for enactment in 2012.

Under the law, companies will be required to offer re-employment to workers who have reached the retirement age of 62. It will allow them to work until 65 and, subsequently, 67.

'Five years is not exactly the 'lifetime in retirement' people have been promised.'

MR NEIL DUNCAN-JORDAN, spokesman for the National Pensioners Campaign, on the impact of raising Britain's retirement age to 70 on those with a life expectancy of 75, such as low-paid manual workers