If your contractors are direct, you will need to ensure that your payroll function correctly deducts appropriate taxes at source. If they are paid through an agency, you will need to inform the agency of the IR35 determination and be comfortable that they are deducting the appropriate taxes at source. For peace of mind, you may request evidence or conduct regular audits. Your business could be held liable for tax payments and penalties if deductions are not made or are made incorrectly.