After receiving thousands of rejection letters, 60-year-old Anthony Barlow decided to conduct an experiment. He had been on the dole for more than a year and was becoming convinced his age was the reason. So he responded to a job advert with two applications: one with his real age and another with a date of birth of 1989. He edited his years of experience and qualifications accordingly.

It was no surprise when his less-qualified 23-year-old alter ego got an interview, while Barlow was told he didn't reach the required standard. "I do believe there is ageism and now I've tested it," he said. "I almost feel like giving up. Young people can't get employment, so what chance have I got?"

Barlow has been out of work since May 2010 when his Threshers off-licence franchise closed following its owner's collapse. He had remortgaged his home to fund the venture and now Barlow and his wife are left with £24,000 in debts.

He has had odd cleaning jobs over the past two years but despite thousands of job applications and more than 20 years of retail industry experience, he has failed to find full-time work. His debts have increased and his mental and physical health have deteriorated as the months have gone by.

"I want to work. I have never been a malingerer. I can't stand sitting around. The boredom sets in and you say to yourself: 'Where's my whisky?'"

Barlow is not alone. The over-50s are the worst-hit age group when it comes to long-term unemployment. It is a trend that economists warn will cost the economy dear as the population ages.

Because of the stalled economic recovery the problem is getting worse. The number of over-50s out of work for more than a year has doubled since the start of the recession to stand near a 15-year high, according to official statistics.

This week's data on the labour market is unlikely to bring much hope to Barlow. But the political and media focus will again almost certainly be on the record 1 million young people out of work. "There's huge political capital with young people … but the most important thing is not to forget about over-50s," said Ian Brinkley, director of thinktank the Work Foundation.

The older worker had not fared too badly over recent years, he said, and there were more over-50s in work now than before the recession.

In that sense, it is understandable that much of the political and campaigning focus is on youth unemployment and the lasting social scars it can cause. But once unemployed, older people are far more likely to stay that way. "Once you are out of work and have been out of work for some time your chances of getting back into work go down," Brinkley said.

Official statistics underline that. Almost half of those over-50s who are unemployed have been out of work for more than a year. That compares with a quarter of unemployed 18- to-24-year-olds. Economists blame the problem on a combination of factors: employer prejudice, health issues and the relative difficulty in relocating to new jobs as older workers tend to be tied down by mortgages and other commitments.

But with people living longer and the pension age rising, leaving older workers on the jobs scrapheap is more than a social issue, experts warn. By 2020 a third of the working-age population will be over 50. If employers are reluctant to hire them, there could be huge costs in benefit payments and lost spending power. There is also the loss to employers as they struggle to fill vacancies.

UK employers are expected to need to fill around 13.5m vacancies in the next 10 years but only 7 million young people will leave education over that period, says the Chartered Institute of Personnel and Development (CIPD). It argues that immigration alone will not fill the gap and that employers will increasingly need to rely on older workers.

The CIPD has just published guidelines for workers and employers on how to manage older workforces, including how to change attitudes and make the most of all workers' skills. "Organisations that respond appropriately to the challenges of an ageing workforce will gain a significant competitive edge," said Dianah Worman, the CIPD's diversity adviser. "The business case for older workers is strong and research shows their impact and experience within the organisation enables better customer service, enhanced knowledge retention – and can help to address talent and skills shortages.

"All of this will help to guard against potential age discrimination claims, thereby mitigating damage to the brand and any associated costs."

Some employers have already recognised that, perhaps the best-known example being retailer B&Q, which was among the first to target older workers.

But labour market experts worry that with the focus currently very much on youth unemployment, employers will in future take on younger workers, especially if given incentives from government.

The Age and Employment Network (TAEN) is campaigning for earlier intervention to cut back long-term unemployment. At the moment, most over-50s have to wait 12 months to be referred to the government's Work Programme.

If older people do get on to the programme, their needs are not always addressed by the agencies running it, said TAEN's chief executive, Chris Ball. "It's important all these organisations think very carefully about how they can make their staff effective to older workers and I am not sure that many have given much thought to that problem because there is this stereotype of the younger jobseeker," he said.

Barlow agrees. He has been visiting an agency near his home in Hampshire for months. "The first time I went I was told my first assignment was to keep the next appointment. It's like playschool."

The job interviews he does get do not sound too far off playschool either. "Everything is different to how it was years ago. They sit around a table blowing balloons up and building things."

Barlow's bemusement at the new ways of grilling candidates is something Delyth Evans comes across often. She runs Dress for Success London, a charity helping women back to work. Part of its work is preparing older workers for interviews.

"We are seeing women who had been in the same job for a long time going back into the labour market and having to look for work and finding it very hard. They haven't had to experience interviews, apply for work or think about their skill set. They feel the labour market has changed an awful lot since last time they looked for work and their confidence going into it is low if they are over 50," she said. But she is hopeful that employers are starting to recognise the upsides of hiring older workers.

"We often tell women over 50: 'Stress at interview that you don't have any family commitments, that you are incredibly flexible and won't have to take time off other than holidays.'"

She added: "The message to employers is look at the whole picture. Look past someone's age and realise they will be incredibly reliable and will have a lot of emotional intelligence – and older workers are less likely to move on."

For Barlow, however, the months of fruitless job hunting and visits to employment agencies have left him with very little optimism.

"I've got 10 years of working life left. I used to believe in life before death but now I'm not so sure," he says.