Sharing a house with friends can make sense when you're in your 20s and 30s but it fast loses appeal once you hit your 40s. However, living in a multi-occupancy property and sharing a kitchen, bathroom and living space is the only option for an increasing number of professional fortysomethings.

Of those that rent a room in shared houses, as many as one in eight are in their 40s, according to a study by website Spareroom.co.uk, and that figure is rapidly rising. The number of older professionals – classed as 30 and over – searching for rooms within flat-shares has increased by over 2,000 from 12,000 in the past six months, says flat-sharing website Easyroommate.co.uk.

Perhaps it is no surprise when you consider that the average rent in the UK for a studio is £1,102 a month, according to the latest figures from Rentright.co.uk, a lettings agency directory site, whereas a two-bed property costs £1,218, or £609 per room.

If you share with more than one person the amount you pay drops considerably: a three-bedroom house is around £716 (£238 per room) outside London, and £1,212 (£404 per room) in Greater London, according to mortgage lender BM Solutions.

With demand exceeding supply, the situation is likely to worsen. Already the costs of housing have risen to such an extent that almost a million people have taken out a payday loan to help with their rent or mortgage, the housing charity Shelter has found. It claims the situation is reaching "breaking point" for many people up and down the country.

Kay Boycott, director of communications, policy and campaigns at Shelter, points out that, in many cases, renting is no cheaper than buying a property, but with rents increasing – by 7% in London in 2011 – it is virtually impossible for aspiring homeowners to save a deposit.

"Spiralling house prices and the expense of renting on your own mean that people are left with no other choice than to share a house or flat long after they would have expected," she says.

Research carried out by Rightmove.co.uk for The Observer shows that 17% of first time buyers are now 40 or over. It also found, at the end of last year, that 27% of people who consider themselves to be "trapped renters" (those who want to buy but cannot afford to for a least another year) were over 40.

Aspiring homeowner

Audrey Dixon is a classic "trapped renter". At 40, she's living in a flat in the Ruislip area of London with a 22-year-old flatmate who she found through Easyroommate.co.uk. "Splitting the household bills, as well as the rent, is what helps reduce my monthly outgoings so much," says Audrey. "But as everything is getting more expensive, it's taking even longer to save for a deposit."

Audrey, who works as a housing officer, adds: "Single people are basically priced out of the housing market at the moment, particularly in London, and doubling up is the only practical way to keep costs low. Fortunately, it works out fairly well for me because I happen to get on so well with my flatmate.

"But unless something dramatic happens in the housing market I'll be living in shared houses for years because there's no way I can afford to get on the property ladder."

When they do come to buy, those in their 40s and over, face particular difficulties, according to David Hollingworth of mortgage broker London & Country. He says: "Older first time buyers age are looking at a shortened term in which to repay their mortgage and it's hard to save for a deposit while you're renting, yet many lenders demand at least 10% of the value of the loan, and more than that for better rates.

"While there are options out there, such as the government's NewBuy scheme and shared ownership, there's a whole generation who may actually never be able to afford to buy a home."

Single but sharing

Shelter says that 235,000 Londoners have moved in with a partner for mainly financial reasons over the past three years – with 128,000 forced to continue sharing after their relationship ended. It's a struggle for those that do decide to separate: being single is a major factor in forcing many fortysomethings to continue sharing.

Catherine Swan, 49, has lived in shared accommodation for the past six years since relocating to London. Her landlord is selling the flat so, reluctantly, she has to find another place, hopefully only with one other person. She expects to have to pay up to £600 a month.

"It horrifies me that I'm still looking for shared accommodation at my age," says Catherine, who works in stage production. "By now, I thought I'd be living out of London, in my own home, and pottering around my garden at weekends. I didn't anticipate that I'd be trawling through adverts for seven-bed houses in Clapham, where people just want to party all week," she says.

"I wish I could afford to rent, or even better to buy, a tiny studio flat but due to the economic climate, I just can't."

Swan has one bit of advice for young people who are still fancy free: "It is being single that makes it almost impossible to either rent a place on my own or to buy a home to live in.

"My advice to any young person is to marry a wealthy partner as soon as they can, as it's the only way to get on to the property ladder. Unfortunately, that advice is as true today as it was in Jane Austen's era."

Weekly commuter

A further factor forcing professionals in their forties into multiple occupancy is having to travel long distances to find work, says Ian Carlton, a HR consultant. While Carlton manages to maintain a mortgaged property in Staffordshire, where he returns to his family at the weekends, he's not happy that the greater part of his week is spent in shared accommodation.

Working long hours in the City of London Monday to Friday means he needs a place to relax in the evenings and, at 46, he'd rather live alone. "But there's no chance," says Ian, who shares a flat in Rotherhithe with another man in his forties. "The cost is completely prohibitive. At first, I thought it was really sad of me to be sharing a place with someone I didn't know.

"But it was the only way to get a semi-decent place and, as it happens, my flatmate works long hours, too, and fortunately we do get on well when we see each other.

"It involves compromise. One of us can't watch the football if the other wants to watch The Apprentice. I didn't think I'd have to be working out things like that with a flatmate at my age."