Local authorities are having to spend millions of pounds on social work agencies as they struggle to recruit permanent staff, with some authorities employing nearly half of their children’s social workers through private companies, a Guardian investigation has found.

Data obtained through freedom of information requests shows that many English councils are routinely spending tens of millions of pounds – a total of at least £335m in 2017/18 – hiring agency social workers.

Experts said the difficulty experienced by councils in attracting permanent staff meant vulnerable children and families were often seeing multiple social workers in a single year, making it harder for them to engage with services.

They said the large-scale use of agency social workers was a poor use of dwindling local authority funds, as locums received a higher hourly rate than permanent staff, on top of the fee paid to the company they were employed through.

An overwhelming majority of social workers say spending cuts are affecting services and putting added pressure on care professionals, exclusive Guardian research reveals.

Some 92% of social services staff who took part in the Social Lives survey highlighted the impact of austerity, while 88% say social work isn’t as high on the political agenda as other public services.

The research, conducted by Guardian Jobs in association with Affinity Workforce, asked more than 1,420 staff across the social work profession about their working lives and revealed that although the majority get real satisfaction from their jobs, they face huge pressures every day.

As one survey respondent put it, social workers feel they are performing “mission impossible on a daily basis”.