They are the “sandwich generation” - middle-aged men and women who are caring for their children and maybe grandchildren as well as their elderly parents.

Their numbers are likely to grow after official figures published yesterday projected a rapidly ageing population, a high proportion of whom will be frail and vulnerable.

Nearly one in four of the population will be over 65 in less than 25 years, and the number of those over 85, known as the “oldest old”, would more than double.

The projections from the Office for National Statistics point to greater demand for health and social care, changes to the design of homes and transport policies that recognise the needs of elderly people.

Millions of people are living longer as a result of medical advances and improved social conditions and the ONS said that a younger generation would have to work longer to pay for the retirement and care of the greying population.

The ONS said that the number of people expected to live more than 85 years would rise to more than three million by 2032. It added that the number of people with dementia could double to 1.4 million within 30 years.

Karen Dunnell, a national statistician, said: “By 2032 the 85-plus group will make up 4 per cent of the population. That means the proportion of people who use public services the most and who depend on family, neighbours and so on is increased.”

The report by Ms Dunnell said that increasing the retirement age was the key to supporting the millions of extra older people who will need assistance.

But increasingly men and women will face the dilemma of how to look after their elderly relatives when they themselves are reaching retirement.

Ms Dunnell said: “Children caring for their parents will be increasingly old themselves and potentially caring for their children or grandchildren at the same time as their ageing parents.

“Demand for long-term care is inevitably going to increase over the coming years as the population aged 85 and over grows.”

There will be additional problems arising from the breakdown of families. “The rising numbers of older single people and the break-up of families through divorce are likely to reduce the provision of informal caring,” Ms Dunnell cautioned in her annual article on Britain’s population.

Charities for older people said that the consequences of an ageing society would be far-reaching and that society was burying its head in the sand about the practical measures required to meet the needs of the elderly.

Help the Aged said that there needed to be more public transport and the routes would need to pass doctors’ surgeries and hospitals rather than simply schools and workplaces.

Houses would have to be built so that they could be easily adapted for the elderly, Kate Jopling, of Help the Aged, said.

“It is going to make sense to build homes in a such a way that there could be a downstairs bathroom, with wider doors for wheelchair use, fewer steps, electrical sockets installed at waist level and stairs that can easily take a stairlift.”

Ms Jopling said that people had to be much more realistic when coming up to retirement about how much longer they might live and their future care needs.

“The idea of living in a beautiful cottage might be a good idea when you are young but people need to think about the future, about living until they are 80 or 90.

“One of the problems we have is that people still widely underestimate their own longevity. They cannot accept they are going to live until their late eighties or even longer.”

Several parts of the country already have a high proportion of elderly people, the figures showed. East Dorset, North Norfolk, Rother in East Sussex, West Somerset and Christ-church, Dorset, have a pensionable population of more than 30 per cent.

Clare Steel, the head of adult social care at Somerset County Council, said that it was increasingly difficult to find younger people willing to do the work that older people require, such as gardening and care in the home.

The council organises a volunteer car driver service in which people are paid mileage to transport the elderly. When they can no longer get in and out of a car, the council provides transport for those in wheelchairs.

She also said there would need to be a growing amount of “extra care housing”. This is accommodation where an individual is in purpose-built premises in which they are helped to get up and provided with “light-touch” supervision but remain in their home.

Yesterday’s breakdown of figures show there were 9.5 million over65s in 2007. By 2032 the figure is projected to increase to 16.1 million, 23 per cent of the estimated total population.

In 1982 there were 600,000 people over 85, or 1.1 per cent of the total population. By last year this had doubled to 1.3 million and will rise to 3.1 million by 2032.

In spite of the growing number of old people, the proportion of over65s living in communal establishments fell between 1991 and 2001 as a result of government policies to support people in their own homes and communities.

The analysis also showed that men are living longer and closing the life expectancy gap with women.

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