Social work staff are exploited - Unison
Support workers and assistants are routinely used as "social workers on the cheap", a union has claimed.
Unison said two-thirds of 350 support staff it surveyed were regularly given work with vulnerable children and adults they were not qualified to do.
The system needs "proper safeguards", the public sector workers union said.
The Association of Directors of Children's Services said staff should raise any concerns about unsuitable work with a supervisor or manager.
The government is trialling social worker-led practices - independent of councils - which it says allow social workers more time with individuals.
Unison says that although there has already been some reform, the system is too reliant on support workers who can be out of their depth when left to work alone on complex cases.
Helga Pile, the union's national officer for social care, said there were not enough qualified social workers, resulting in support workers being used as "cheap labour".
"Assistants and support workers are seriously struggling to cope with the pressures being piled on them, as demand continues to grow, while resources are drastically cut," she said.
"Staff are very concerned about vulnerable children and adults who rely on the services."
She added: "Staff are very concerned about vulnerable children and adults who rely on the services.
"There aren't enough social workers, so they are under growing pressure to step into the breach and carry out work they may be unqualified to do. They end up suffering from excessive bureaucracy, stress and burn-out."
The survey found three out of four worked extra hours, while two-thirds earned less than £21,000. Half of those polled had suffered verbal attacks and one in four had received threats.
Matt Dunkley, president of the Association of Directors of Children's Services, said: "Social work assistants should not be given tasks that they feel unsure of or unqualified for, and such concerns should be raised in supervision and with team managers.
"Local authorities will be looking for innovative ways to deploy their staff to ensure children are safe and that children in care are well looked after, as well as protecting budgets as far as possible to meet rising demand.
"This means ensuring that specialist staff are available for the most vulnerable children and recognising where some tasks can be done by an unqualified worker under the supervision of a senior social worker.
"In doing this, managers should consider both the letter and spirit of regulations about social work tasks, ensuring that assistants feel well supported and are not given high risk cases."