RIDDOR stands for the Reporting of Injuries, Diseases and Dangerous Occurrences Regulations. This 2013 legislation requires that you report workplace incidents. A report should be made no later than ten days after the occurrence.
Reports are made to the Health and Safety Executive (HSE). They should be made by a responsible person such as a supervisor, manager or business owner. Not all incidents need to be reported, though a majority do. You should file a RIDDOR report online.