A recruitment crisis in children's services and safeguarding has resulted in Wirral Council spending more than £400,000 per month on temporary agency staff.

The high cost reflects a problem in retaining social workers across England.

Local authorities are relying on agency workers to cover nearly 4,000 out of 5,500 otherwise empty posts.

It means almost a fifth of all children's social worker jobs are vacant.

In February Wirral spent £512,000 with the Matrix agency, 86% or £440,000 of this was to supply temporary social workers mainly for children's care and safeguarding.

National figures show the average cost of an agency social worker is £1,250 per week.

Representatives from local authorities told a recent parliamentary select committee that social workers are leaving for better pay working as agency staff.

And they are also under constant pressure because of media coverage and criticism of their role in high-profile cases such as the death of Ayeeshia Jane Smith.

A spokesman for Wirral Council said: "We have to ensure that we have enough social workers to work alongside and safeguard vulnerable Wirral people.

"In recent years we, like many local authorities, have faced challenges recruiting full-time social workers - and a key aspect of maintaining a high level of support has involved employing temporary, skilled agency staff.

"Bringing in short and medium-term agency support like this is a valuable way of filling the gaps.

"We have undertaken a recruitment exercise for social workers already this year, we currently have a new advert out and we will continue to recruit on an ongoing basis in order to reduce the amount we spend on temporary social work staff.

"Wirral is part of a Merseyside-wide collaborative exercise with other local authorities designed to manage the amount we spend on temporary staff and ensure value for money."

Some councils are resorting to desperate measures to recruit full-time care workers.

Derby City Council is offering new social workers £10,000 towards their mortgages in the first incentive scheme of its kind in the UK.

The council says the £200,000 taxpayer-funded "golden door-key" deal will save money in the long-term as they attempt to cut back on expensive temporary workers.

The authority claims it cannot compete with "considerable" agency salaries, so are instead trying to lure in employees through the housing package.

Under the plan new employees will get a loan towards a mortgage after a six-month probation period, and if they stay in their job for five years it will not have to be repaid.

The Government’s recent spending review promised up to £3.5bn extra cash for social care by 2020.

This included up to £2bn through new council tax raising powers.

However the Local Government Association questioned the figure, instead putting the sum at £1.7bn annually.

It also raised concerns that the move is “regressive” because more deprived areas will be least able to raise income through council tax.