In the first official projection of its kind, the Department for Work and Pensions today forecasts that almost a fifth of Britons will celebrate their 100th birthday.

　　Of the 17 per cent of the population who will become centenarians, about three million are under the age of 16, and 5.5 million are aged between 16 and 50.

　　The statistics show that there are 1.3 million 51 to 65 year-olds who are likely to get their royal telegram, along with 875,000 people who have already retired.

　　In total, about half a million people a year will be celebrating their 100th birthday by 2066, compared with about 10,000 now. Nearly 8,000 of them will reach their 110th birthday.

　　Last night, Steve Webb, the pensions minister, urged workers to begin saving for their retirements as soon as possible. Mr Webb is trying to introduce significant reforms to the pensions system. "These staggering figures really bring home how important it is to plan ahead for our later lives," he said. "Many millions of us will be spending around a third of our lives or more in retirement.

　　"That's why we are reforming the pension system to make it sustainable for the long term, making sure people can look forward to a decent state pension when they retire, and helping millions save into a workplace pension, many for the first time."

　　Experts said the rise in those aged over 100 years old – the fastest growing age group – has profound social, economic and financial implications.

　　Taxpayers face an increasing bill to meet the pension and health care costs of the elderly.

　　Individuals will have to work later, sell their assets and put more money aside throughout their lives to fund retirements that could last more than 30 years.

　　Ministers have considered linking the state pension age to life expectancy which could see future generations working into their seventies.

　　Ros Altmann, the director-general of the Saga Group, said: "Pension funds were never designed to cater for lots of people living to 100. We have got more and more people who are going to live longer with much less money and something has to be done about it."

　　Official research has also found that most Britons expect to die earlier than is likely to be the case.

　　In 1981, there were 2,600 centenarians but this is forecast to rise to more than 280,000 by 2050.

　　There has already been a 70 per cent rise in people living to 100 since 2000, with six women to every man in this age group.

　　The rich and those living in southern England typically enjoy longer lives.

　　As people are living longer, ministers are trying to encourage workers not to opt out of new workplace pensions to be introduced next year.

　　Most workers retire with a pension previously intended to fund a retirement of 10 or 20 years – rather than an extra 30 years of life. For example, savings of ￡100,000 would pay out at least ￡5,000 a year for two decades, but less than ￡3,500 over three decades. Under the "auto enrolment" scheme, all workers will be offered a pension to which their employer will make some contributions.

　　However, people can ask to leave the pension.

　　The Government has previously declined to cut universal benefits offered to pensioners and will increase the state pension in line with wages, rather than inflation, from next year.

　　Some experts believe that such measures will become increasingly unfair on younger generations.

　　Life expectancy for babies and those retiring has confounded experts, rising more quickly than expected.

　　Average life expectancy for a newborn girl is now 81 years and nine months, while for boys it is 77 years and seven months.

　　More than a quarter of newborn boys 30 years ago were expected to die before their 65th birthday, compared with 15 per cent today