Employers' liability insurance is required by law if you hire staff, even if they are part time or temporary. Site workers can be at greater risk of accidents due to the nature of the work they do, particularly when working with plant and machinery. Having this cover in place can protect your business against the financial exposure of personal injury claimed from employees; insurers usually offer £10M protection as standard.
You will need Employers’ Liability if you have an apprentice, or even if you have a volunteer who works for your business. The only exemption to this is if the employee is closely related to the owner and the business is not a limited company. Even so, it would still be prudent to purchase Employers Liability insurance to cover yourself and your business.