Some of Britain's leading children's authors are calling for a radical redesign of the child protection and child mental health systems, warning that the current system is failing the country's most vulnerable and neglected children.

A group of writers, including Philip Pullman, Francesca Simon, Lauren Child and Patrick Ness, have signed a letter backing a campaign spearheaded by the London-based children's charity Kids Company for a wholesale reorganisation of children's mental health and social services.

"We find it unacceptable that Ofsted has declared that one in seven councils in England fail vulnerable children with 'unacceptably poor' standards, within a structure described as 'manifestly and palpably weak,'" the letter states.

"As writers for children, our job includes inspiring our readers and encouraging them to understand the potency of imagination and thought, in the hope that when they grow up they can use them to help improve the real world. As taxpayers and adults committed to the welfare of children, we are saddened by the lack of political imagination which has led to millions of children in this country who are abused, neglected and/or suffering from mental health difficulties being denied appropriate care."

The writers cite a recent survey of social workers by the publication Community Care, which revealed that 73% of social workers questioned said they were unable to do their job properly, leaving children at risk because demand outweighs resources.Their unusual intervention came as the founder of Kids Company, Camila Batmanghelidjh, launched an independent taskforce to design a new way of delivering child protection and child wellbeing services. The former director of public prosecutions, Keir Starmer, will chair the body, and will be joined by the children's commissioner, Maggie Atkinson, and the chief executive of Lambeth council, Derrick Anderson.

Batmanghelidjh said she was motivated by a sense of frustration developed over 30 years working with neglected and abused children, and seeing little improvement in the state support available for them.

"Fundamentally, things have not improved. Even governments that intend to support vulnerable children get hijacked by other agendas when they come to power. Vulnerable children get relegated to the bottom of the political pile, and no one is holding the government accountable on their behalf," she said.

Senior social work professionals and child mental health workers had told Batmanghelidjh repeatedly that they felt they were unable to give the children they worked with the support they needed because of funding constraints. Her desire to restructure the current system "should not be seen as an attack on social workers", she said, but was aimed at reforming the system that often made it hard for professionals to get children support.

She proposes creating a "department for family resilience" that would bring together child mental health teams with social services, youth justice and special needs services. "Who says that we should keep social services and child mental health separate. Is that a good idea? Who says that psychiatrists should stay in clinics, and we should assume that they will have a parent that will take them to the appointment? Is that a good construct for a child whose original problem is a lack of commitment and care?" she said.

Local authorities are often reluctant to capture the real level of need among children and young people in their locality, she said, because they lack the capacity to meet that need, and in identifying it they would be legally obliged to address it. The taskforce would try to pin down accurate numbers of children who need support.

A report published by the Centre for Social Justice (the right-leaning thinktank founded by the secretary of state for work and pensions, Iain Duncan Smith), Enough is Enough last month said many child protection and mental health services were in crisis, and warned that the point at which many vulnerable children qualified for help was set too high.

But Alan Wood, the president of the Association of Directors of Children's Services (the professional body for senior managers in children services) said he did not see the need for a radical restructuring of the current system.

"It is very easy to extrapolate from a modest evidence base failures in the system. Day-in, day-out, thousands of dedicated staff are working successfully with hundreds of thousands of the most troubled and troubling children, and that should not be overlooked. The challenges facing children's social care are more acute than ever before, especially in a climate of diminishing resources and increasing demand," he said.

Last year, over half a million children in England were referred to children's social care with nearly 53,000 children becoming subject of a child protection plan and in excess of 375,000 children designated as children in need.

"We need to improve the system where it is failing but we don't believe the system is failing as a whole," Wood said.