Dozens of childcare groups in London have failed to properly safeguard children.

The revelation will alarm many parents who have put their children in nurseries, crèches, after-school club and holiday play schemes.

Ofsted found 143 centres caring for children in the capital to be "inadequate" in 2007/08. Some of them are run privately, others by volunteers, church groups or town halls.

Many parents pay about £200 a week per child for a full-time nursery place or up to £50 for 15 hours a week in an outofschool club.

But the education watchdog discovered weaknesses in carrying out Criminal Record Bureau checks, an unsuitable adult linked to one centre and failures to check references for new staff.

The 143 centres represented about eight per cent of the 1,691 inspected by the education watchdog between 1 April last year and 31 March this year. It compares with six per cent in the previous year.

Ofsted inspectors based each rating on a series of categories including helping children to be healthy, protecting them, nursery education, children's achievements, and organisation.

Some were found to be at least " satisfactory" in nearly all of these areas but were still classed as "inadequate" because of a specific issue. Others failed in a number of the categories.

Ofsted identified weaknesses in carrying out Criminal Records Bureau checks and failures to check references for staff. An "unsuitable" adult was discovered at one centre. Other findings included:

• Children were "not sufficiently nourished" at one after-school club.

• At two other centres children were at risk of dehydration.

• At another group, staff often fed their charges with their fingers.

• Poisonous plants were found in the garden of one nursery.

• Sharp knives were easily accessible to children from a drawer in the kitchen at an after-school club.

• Toxic fluids were not stored out of the reach of children at another club.

• At some centres, people were allowed to wander in because doors were left unlocked or open.

• Staff at one after-school club failed to pick up children from school on several occasions.

At other centres, babies were not given enough cuddles and were left to play with dirty toys; children fell asleep at tables; and staff struggled to stop them falling off their chairs because they were holding a baby. Some children were left unsupervised or were watched only by unqualified staff.

Children's health was put at risk by inaccurate recording of the medication given to them, and by shortages of workers with first-aid qualifications.

Inspectors also found examples of poor hygiene, including toothbrushes stored close to nappy bins and staff and children not washing their hands.

Aplaygroup did not have any batteries fitted in a smoke alarm and the main fire door at one after-school club was obstructed. Concerns were also raised about exposed electrical sockets.

Inaccurate registers increased the risk to children in case of evacuation.

Emma Knights, chief executive of childcare charity the Daycare Trust, said: "These reports will, understandably, worry many parents using childcare but there are many childcare settings offering high-quality care and education."

Shadow children's secretary Michael Gove added: "Parents have a right to expect the highest standards from professionals looking after their children.

"Far too many children were in nurseries which just don't measure up. I share the disquiet many parents must feel."

One centre criticised by inspectors was the £45-per-day Rainbow Village Nursery in Lavender Hill, Clapham.

Parents considering sending their children there said they were concerned at the findings. Billie-Jo Hunter, 35, from Clapham Common, has a four-year-old son and two-year-old daughter. She said:

"I'd be appalled to think I was leaving my children with people who didn't provide the highest standard of care."

Susan Davids, 41, from Clapham Junction, who has a seven-month-old son, said: "I'm not wasting my hard-earned money on somewhere that can't look after children properly. Nurseries cost a fortune. Not giving them enough to drink is a disgrace and letting them be near poisonous plants is terrifying." The nursery said all the issues raised in the Ofsted report had been addressed. There is no evidence that other centres had failed to take action over Ofsted's concerns. Groups contacted by the Evening Standard said they had dealt with the issues.

More than 30 have had further inspections and were found to have improved. A small number were ruled "inadequate" for a second time. Some disputed Ofsted's findings, arguing that it was imposing unnecessary red tape.

Ofsted said it carefully monitors nurseries judged inadequate and checks to make sure improvements put in place. If this does not happen, the local authority can be called in or the education watchdog can launch enforcement action.