if a worker is supplied by an employment agency to an end user it is possible that he or she will not be an employee of either the agency or the end-user and therefore will not be able to claim those employment law rights which are open only to employees;

and an example of a case in which:-

an employment agency was not acting as agent for the end-user in supplying the services of a worker to the end-user

For relevant general notes go to employment agencies/employment status of staff