The rules here are for England, Scotland and Wales.
Who is responsible for what
The agency that supplies a worker is often their employer. The business that directs the work and controls the premises, the end user, is best placed to manage the risks, so HSE treats day-to-day responsibility for health and safety during the assignment as the end user's. So far as is reasonably practicable, you must protect everyone your work affects, including agency and temporary workers, and you should not assume the agency will cover it.
Before the work starts, the agency must liaise with you to identify the risks and agree the actions you will take to control them. It should not place a worker unless it is satisfied their health and safety will be protected. Agree who does what, so that nothing falls between you.
If you take on short-term staff directly, without an agency, they are your employees and you owe them the same duties as to any other employee.
Your risk assessment must cover agency and temporary workers. Regulation 3 requires you to assess the risks to people not in your employment, as well as to your employees, that arise from running your business.
Tell the agency what the job needs
Tell the agency and the workers about your risks
Anyone working in your business who is not your employee must also get appropriate instructions and comprehensible information about the risks to them from the way you run it (regulation 12(3)). Make sure they can identify the people you have nominated to run an evacuation (regulation 12(4)).
Give them an induction on the first day
Brief agency and temporary workers on your site before they start work. Cover the hazards, your emergency procedures, first aid and fire arrangements, who supervises them and how to raise a concern.
Supervise them closely at first. New and inexperienced workers need more supervision, as do people whose first language is not English.
Provide personal protective equipment
The duty to provide PPE falls on the worker's employer under their contract. For an agency worker that is often the agency, but it can be you, so agree who supplies the equipment, trains the worker to use it and replaces it. The worker must not be charged for it.
Report accidents
If an incident involving an agency or temporary worker is reportable under the Reporting of Injuries, Diseases and Dangerous Occurrences Regulations (RIDDOR), someone must report it. Where the agency employs the worker, it is the legal employer and has the usual duty to report. In other cases the duty falls on you as the end user, because you control the premises where it happened.
Breaching the Management of Health and Safety at Work Regulations 1999 is an offence under section 33 of the Health and Safety at Work etc. Act 1974.
Legal basis
Primary legislation and key regulations
Official guidance
HSE - Health and safety for gig economy, agency and temporary workers (opens in a new tab)
HSE · Great Britain
HSE - Managing for health and safety (opens in a new tab)
HSE · Great Britain
Extended scope of the Personal Protective Equipment at Work Regulations (opens in a new tab)
HSE · Great Britain