Families have been priced out of rental property in the majority of local authorities in England, according to the homeless charity Shelter.

The Shelter Rent Watch found that average private rents were unaffordable for ordinary working families in 55% of local authorities in England. Typical rents charged by private landlords were more than a third of median take-home pay, the widely accepted measure of affordability.

Shelter said research showed that 38% of families with children who were renting privately had cut down on food to pay their rent.

Although renting has traditionally been regarded as a cheaper alternative to home ownership, the credit crunch and high house prices have forced many potential homebuyers to remain as tenants.

At the same time, growing numbers of people who would normally qualify for social housing have been pushed into the private sector by an acute shortage of local authority and housing association property. The number of tenants renting privately has increased by nearly one million in the past five years.

The increased demand has pushed up rents, particularly in London boroughs, which are the most expensive in England. At £1,360, an average rent for a two-bedroom home in the capital is almost two-and-a-half times the average in the rest of the country (£568). The least affordable local authority area outside London is Oxford, where typical rents account for 55% of average earnings.

Tenants on benefits in these areas are already having problems finding properties to rent within the new local housing allowance limits, implemented in April for new tenants and from the beginning of next year for those in existing tenancies.

Shelter said tenants in many rural areas were also bearing the brunt of high rents and low earnings.

It found it is cheaper to rent in Manchester, Liverpool and Birmingham than in north Devon, north Dorset or Herefordshire. In Yorkshire, properties in Bradford and Sheffield are more affordable to rent than in the rural areas of Ryedale and Richmondshire.

Shelter's analysis showed that in England 8% of local authorities were extremely unaffordable to rent in, with a median rent of 50% or more of median full-time take-home pay; 21% were very unaffordable with a median rent equivalent of 40% to 49% of median full-time take-home pay; and 29% were fairly unaffordable with the median rent equivalent to 35% to 39% of the median full-time take-home pay.

Campbell Robb, chief executive of Shelter, said: "With huge differences in affordability across the country, there are now worrying signs that families are likely to be displaced by our out-of-control rental market.

"We have become depressingly familiar with first-time buyers being priced out of the housing market, but the impact of unaffordable rents is more dramatic. With no cheaper alternative, ordinary people are forced to cut their spending on essentials like food and heating, or uproot and move away from jobs, schools and families."

Robb said it was time for the government to urgently consider how private renting could become a stable, affordable option for families "and not a heavy financial burden that makes parents choose between buying food for their children and paying the rent."

Alice Barnard, chief executive of the Countryside Alliance, said the lack of affordable housing to rent or buy was one of the most pressing issues facing rural communities.

"The countryside has seen its population grow at twice the rate of urban areas, which has driven up prices, forcing families to make sacrifices to meet spiralling rental costs and pricing young families out of the communities in which they have grown up," she said.

"If we want our rural communities to flourish then the government needs to urgently review the rental market in rural areas to enable rural communities to meet their housing needs."

Melissa Brown, a part-time yoga teacher, and her husband David*, a college lecturer, found it impossible to rent a decent affordable property when their landlord decided to sell their existing home.

The couple, who live in Brighton with their three children, had been renting a three-bedroom terrace house for £1,250 a month for two-and-a-half years but last January were told they had to move out because the landlord wanted to sell up.

It took them six months to find somewhere that was still close enough to their children's school and they ended up moving in September into a three-bedroom house for £1,550 a month.

The house is in a poor state of repair with damp and needs decorating and other work, but Melissa said that most of the properties they looked at was "eye-wateringly bad".

"Most of the rented houses around here are not suitable for families because the lounges have been turned into bedrooms so landlords can put students in there and make more money. Even groups of professionals are living in shared houses with no lounge," she said. "We've been renting for years and it's never been as bad as this. It's all driven by greed."

She added: "We did ask about repairs to this house and the landlord is paying for paint, but she has been told she could rent the house out to students for £1,650 a month and already thinks she's doing us a favour."

Their couple's household income is about £2,000 a month and they are already really struggling to make ends meet.

The family is planning to use the loft area as an extra bedroom for a lodger to raise money. Melissa said: "The landlord doesn't mind how we raise the rent, so we are considering becoming landlords ourselves. If you can't beat them join them."

*The names have been changed in this case study