If you have more than 10 employees or own or occupy a mine, quarry or factory, you must keep an accident book under social security law.

Keeping records of incidents helps you to identify patterns of accidents and injuries, so you can better assess and manage risk in your workplace.

Records can also be helpful when you are dealing with your insurance company.

Make sure you protect people’s personal details by storing records confidentially in a secure place.

From: https://www.hse.gov.uk/simple-health-safety/reporting-accidents-ill-health.htm