HMRI stands for
Her Majesty's Railway Inspectorate
HMRI is a division of the Health and Safety Executive (HSE), specifically charged with maintaining the health and safety of both the workforce and passengers on Britain's railway network.
As such, they are responsible for conducting reports into the causes of train crashes and other rail incidents. They publish information on such incidents on their webpage, which contains a list of all railway accident investigations, including a monthly report of 'SPAD' incidents.
http://www.hse.gov.uk/railway/rihome.htm