You may need to use one of these forms when sending post:

To make a request for Tracked Service via Royal Mail:

Tracking Request form

To apply for a new internal postal account or replacement departmental stamp:

New/Replacement Stamps form

To safely send chemicals abroad:

CHIP form

To send chemicals (organic or inorganic) to the USA:

Toxic Substance Control Act (TSCA) declaration form
Overview of key TSCA concepts and definitions