By Emma Griffiths BBC News Online

On a former bomb site in south London, families are building their own homes with the aid of some charitable volunteers.

Naomi and Matthew Ashman had almost given up hope of ever owning their own home.

Their four children, aged three to 13, were sharing one bedroom in a Bermondsey council flat, which the couple have lived in for the past 21 years.

Even with their right-to-buy discount, the �92,000 price tag was out of their reach.

The Ashmans helped build their own house

They are not alone.

Southwark Council is London's largest landlord, but cannot keep up with demand for social housing.

Rising house prices and rents have forced residents on average incomes to turn to the council for accommodation.

But it already has 13,000 people on its waiting list and last year just 2,500 of its 48,000 properties became available.

It is estimated that 12,000 families in the borough are living in cramped conditions and 97% of council tenants could not afford a suitable mortgage.

The Ashmans have decided to take matters into their own hands and have helped build their own three-bedroom home in Gordon Road, Peckham.

What I'm looking forward to is the kids having their own room, they won't be arguing with each other constantly

Sharon Burnett

They took part in a scheme run by charity Habitat for Humanity which pays for the land and materials through donations and keeps prices low by using volunteers to build homes.

Prospective homeowners invest 500 hours of labour and are rewarded with a house at half the market value and a 20-year interest-free mortgage.

Volunteers ranging from carpentry students to teenagers from the local youth offending teams do everything short of the brickwork and the plumbing.

Even chief executives of investment banks have been spotted digging trenches on the site and many of the volunteers are corporate employees sent along for team-building exercises.

Habitat for Humanity believes it offers a "unique solution" to London's affordable housing crisis.

Southwark's Habitat for Humanity executive director Jeremy Cross said: "Because of its proximity to the City, house prices shot up as have rents in the private sector.

Homes were built on an old bomb site

"People who are unable to access social housing are really trapped in a difficult situation.

"The council is trying its best but is battling to keep up with the needs of an inner city borough."

The three-bedroom houses are now being sold to the chosen families for �65,000 - half the estimated market value.

But they will not be able to take advantage of the booming housing market - houses cannot be sold for a profit for 20 years.

That does not bother Sharon Burnett, whose family have been stuck in a two-bedroom flat on the 16th floor of a tower block in east London's Tower Hamlets.

Sharon, her husband Des, and their three children had been looking in vain for a property they could afford on an income of �17,000.

"We've been down as far as Kent and Folkestone but even there property was out of our reach," said Mrs Burnett.

We think it is a miracle that we are able to afford somewhere to live

Naomi Ashman

"What I'm looking forward to is the kids having their own room. They won't be arguing with each other constantly - it really grinds you down."

Habitat for Humanity needs another �2m to fund another project in Southwark and future developments in Hackney, Tower Hamlets and Newham, all in east London.

It already has 250 families on its books applying to take part in future schemes.

The latest batch of four houses should be complete by the end of January, although Naomi and Matthew Ashman will be moving in before Christmas.

Mrs Ashman says the first thing she will do in her new home is pray.

"We think it is a miracle that we are able to afford somewhere to live," she said.