At least £2.1bn was spent on agency staff by councils across the UK last year, according to analysis by the 4 Day Week Campaign.

Researcher Nic Murray called the spending on agency staff a ‘colossal waste of taxpayers' money'.

Freedom of Information Act requests made by the national campaign group found that for the 2022-23 financial year, councils' spending on agency staff amounted to 6% of their total spend on staff.

The 4 Day Week Campaign said spending on agency staff had been rising year on year, with £1.8bn spent in 2021-22 and £1.6bn in 2020-21.

Slough's spending on agency workers as a percentage of its total staff spending was highest - amounting to 42%.

Earlier this year, the Local Government Association reported that nine in 10 councils across the UK were struggling with job retention and recruitment.

The 4 Day Week Campaign argued that adopting a four-day working week would help councils improve job retention and recruitment.

South Cambridgeshire DC was the first UK local authority to trial a four-day working week, with no loss in pay for staff.

The council said that before trialling the shorter week it was spending around £2m a year on agency staff.

Analysis found that the authority's annual wage bill decreased by £300,000 after the three-month trial.