The guidance can be found below:
www.gov.uk/guidance/off-payroll-working-in-the-public-sector-reform-of-intermediaries-legislation
Public authorities need to decide whether the off payroll working rules apply and the conditions have been met. They will need to deduct income tax and nation insurance contributions if the worker is paid directly, or advise the agency if the off payroll working rules apply before the contract or work starts.
The definition of a public authority includes government departments,agencies and local authorities, companies controlled or owned by the public sector, schools and universities and the National Health Service. Where a public authority has fully contracted out services to a third party and the workers do not personally provide their services to the public authority, then the rules would not apply.