Introduced in 2004 to provide a framework for the minimum standards contractors should expect from recruitment agencies, the conduct of employment agencies regulations are aimed at the temporary workforce and those that are controlled by the end client. Most contractors are businesses in their own right and sit outside of the regulations.
There will be a requirement for contractors to opt in or opt out of the regulations.
Opting in will provide you with workers rights like paid holidays and maximum hour weeks but will make HMRC see you in the light of an employee which will be detrimental to any IR35 enquiry.
Therefore, if you are genuinely in business as a contractor then it is best to opt out of these regulations.