More than two thirds of councils are failing to ensure enough childcare is provided for working parents, campaigners for families' rights have warned.

Just one in five local authorities have enough childcare for parents with children under two, and one in three for school age children, the Daycare Trust and Family and Parenting Institute said.

And just one in seven have enough childcare for disabled children - a figure which has not improved in five years, the charity said.

The research follows recently published Department for Work and Pensions figures that showed a third of parents who want to work more cannot because they are unable to find affordable childcare.

Daycare Trust and Family and Parenting Institute chief executive Anand Shukla said: "Councils across England and Wales are failing families by presiding over a continuing shortage of high quality, affordable childcare."

He added: "Local authorities have a legal duty to ensure a sufficient supply of childcare in their areas, but no doubt their failure to do so is linked to the tight financial squeeze they find themselves in, with ever more austere funding settlements.

"Only the Government can address this situation by investing more in providing support for parents."

The charity's Childcare Costs Survey 2013 also contains evidence suggesting that plans to increase the number of pre-school children that nurseries and childminders can look after will have little impact on childcare costs.

As part of coalition efforts to cut childcare costs, staff are to be able to take charge of six two-year-olds rather than four while the ratio for under-ones will go up from three to four.

But childcare costs for three and four year olds are just 1.9% lower than childcare for under twos, the Daycare Trust and Family and Parenting Institute said.

The charity said the planned changes are likely to exacerbate differences in quality that affect low income groups.

Providers in the most disadvantaged areas are reliant on funding from local authorities, which are increasingly struggling to adequately fund childcare.

As a result, it is children from low income families who are most likely to receive care from providers using the lowest ratios.

Mr Shukla said: "Staffing costs are only part of a complicated picture, so allowing adults to look after more children at once is not only a risky idea, but an ineffective one too.

"With private and non-profit childcare providers exposed to the full force of a harsh business economy, we doubt whether parents will ever see any of the money saved by cutting nursery staff."

Britain has some of the highest childcare costs in the world, meaning many mothers with two or more children find it does not make financial sense to work.

Ministers have still not finalised a much heralded wider shake-up of childcare funding and tax breaks.

The charity's study will be published on March 6.

A Government spokesman said: "Many parents are concerned about childcare costs.

"We are reforming the childcare system so that providers have more flexibility when they have highly qualified staff and childminders are better supported. Ratio changes, which are not compulsory, will allow providers to have the flexibility to increase pay for better qualified workers.

"High quality providers will be able to expand and more childminders will enter the market - this will mean parents have more affordable childcare .

"Ofsted will be the only arbiter of quality, removing any council duplication. As a result more taxpayers' money will go to the frontline.

"We want to help working families with costs and accessibility, and will make an announcement soon."