This depends on whether the basis of your work is labour only or as a bona-fide subcontractor. Labour only means you are effectively a company employee, operating under supervision, and relying on the tools and equipment they’ve provided you to do your job. Bona-fide subcontractors work independently, using their own materials and setting their own hours. If this sounds like you, you’ll need your own insurance—especially public liability, and employer’s liability if you’re accompanied by a team of staff. Most contractors won’t work with you unless you have appropriate cover. It’s also important to check the terms of any master insurance policies if you’re a labour only subcontractor, just in case there’s anything you need to organise yourself.