Agree with Peter but (there is always one “but” isn’t there, don’t you just love RIDDOR)
From the HSE Guidance https://www.hse.gov.uk/vulnerable-workers/agency-temporary-workers.htm
Introduction
….
An "employment business" means the business (whether or not carried on with a view to profit and whether or not carried on in conjunction with any other business) of supplying persons in the employment of the person carrying on the business, to act for, and under the control of, other persons in any capacity.
Agency Workers
If an employment business places a worker for short periods of work with an employer (end user) but the worker remains under a contractual relationship with the employment business, then the guidance for temporary workers applies.
Temporary Workers
There is no single, clear cut definition of a temporary worker as there are often a number of different intermediaries involved, including:
….
An employment business acts as a master vendor and supplies the temporary worker to another business (end user) either directly or via other recruitment agencies (second tier suppliers). A number of different contractual arrangements run in tandem for supply to the same end user
Guidance for Users and Suppliers of Agency/Temporary workers
In many cases the employment business will be the employer of the temporary worker, since it retains ultimate control over their services.
In practice, the day-to-day responsibility for health and safety during the assignment will lie with the end user. It will be in the best position to manage the health and safety of the temporary worker as it will direct the worker’s activities and control the premises where that work takes place….
Accident reporting
Where a worker is not an employee, the duty to report an incident under RIDDOR is on the end user, as the person in control of the premises where an incident occurs.
Hence my comments about who is in control of the person, so it may still be down to the person in control of the premises even if not a direct employee, if deemed to be in control of their activities. Which makes sense to me, but not entirely as clear as Peter notes the Legislation appears to state :0) as it intimates a non-employee’s accident should be reported by the employer (but it seems not always in the eyes of HSE) and hence my comment about confusion.
NB I have highlighted in red key words and the “….” are to show where there is more extraneous text for this point, I have removed.
Chris