The groups give out advice on stimulant drugs and other controversial medical treatments for young children diagnosed with attention-deficit hyperactivity disorder (ADHD). Their internet sites provide extensive details of medications that doctors can prescribe.

But at the same time they are also being secretly financed by the pharmaceutical companies which make the controversial "chemical cosh" drugs.

Last night one of the groups, a government-funded charity, admitted receiving five-figure sums from the drug giants and one of the companies involved conceded that a desire to sell more of its product was one of its motives for providing the finance.

The revelation comes amid increasing concern over the huge increase in children being fed powerful drugs in order to control overly exuberant behaviour.

Prescriptions of methyl-phenidate, a stimulant sold under several brand names, have increased 180-fold in the past 14 years.

Nicknamed "the chemical cosh" for its ability to slow down children, methyl-phenidate is predominantly prescribed to under-16s and its side-effects include insomnia, unresponsiveness and loss of appetite.

Critics claim that its use is unnecessary in many instances, as the children are exhibiting natural traits for their age which can be alleviated with dietary measures.

The National Attention Deficit Disorder Information and Support Service (ADDISS) is a Department of Health-funded charity set up to "provide people-friendly information and resources about ADHD" and its website provides a factsheet giving details of the drugs that can be supplied to children.

It has received funding from three of the major pharmaceutical companies that make methylphenidate and other ADHD medications, which have been accused of sparking suicidal behaviour and liver problems in children.

However, the drug firms' financing is not acknowledged on the site and nor do their names show up on the accounts lodged with the Charity Commission.

Andrea Bilbow, the founder and chief executive of ADDISS, admitted that her group had solicited and received total funding of around £20,000 from Janssen-Cilag, which makes Concerta, a form of methylphenidate, UCB Pharma, which also produces another branded form of the drug, and Eli Lilly, which makes a form of atomoxetine, another ADHD drug which is linked to an increased suicide risk in children.

She said: "From time to time we do go to the pharmaceutical companies to ask for money, but we are not getting massive amounts. We don't sell our soul to the devil but we can't survive without them."

Ms Bilbow said that she did not identify the companies which have funded her charity on its internet site because to do so would be giving them "something in return".

"If we put the names on the site that would be promoting the companies and I've told them I won't do that," she said. "That would be advertising and I'm not getting enough money from them for that."

Another website, Adders.org, run by the Thanet ADDers non-profit support group, also gives detailed instructions on which drugs are available. Thanet ADDers has received money from at least one drug company. A spokesman for Eli Lilly confirmed that it had provided support in the form of a "small grant". Caroline Hensby, who runs the website, did not respond to calls.

The Eli Lilly spokesman said that the company wanted to help educate people about ADHD, but she conceded that there was a degree of self-interest in it doing so.

A spokesman for Janssen-Cilag confirmed that financial support had been given to ADDISS for a "specific meeting" organised by the charity.

A spokesman for UCB Pharma said: "Whilst we have good working relationships with ADDIS and Adders, we have not provided any significant funding or sponsorship."

Not all ADHD help groups take money from the pharmaceutical companies.

Glenn Slater, who has a child with ADHD and runs the website ADDvice.co.uk, which does not receive such funding, said: "Pharmaceutical companies giving money is not a good idea as people on the outside might get the wrong idea about the sites' motives."

Jim Mackie, former chairman of the Overload Network, which provides support for families affected by ADHD, said: "If they [the charities] are being funded by drug companies who are interested in promoting their products then that should be made clear on the websites."