The MCPD (Medium Combustion Plant Directive) is EU legislation that became UK law in December 2017. It sets emissions targets for power-generating facilities with a capacity between 1 and 50 MWth. These currently fall between two other directives that cover large combustion plants and small appliances. Large combustion plants over 50 MWth are covered by the Industrial Emissions Directive (IED). Boilers, heaters and smaller appliances under 1 MWth are covered by the Ecodesign Directive (CE labelling).
This simple questionnaire should tell you if and how you are affected: