Contractors must not be ‘part and parcel’ of the client’s business as if they were one of their employees. They should not be on any internal lists of employees or have business cards showing their client’s name and, crucially, must not be entitled to any benefits offered to the client’s own staff, i.e. bonuses, pensions, and use of facilities such as a gym.
Any clauses that stipulate that a contractor will be subject to performance reviews or disciplinary action (as would be expected of employees) would cause a contract to fail an assessment.