Official UN3373 Regulation Resources
Alpha Laboratories advises all users to consult the official bodies responsible for safe transport of hazardous material.
IATA
The absolute rules for shipping Dangerous goods by air.
http://www.iata.org/whatwedo/cargo/dgr/Documents/infectious-substance-classification-DGR56-en.pdf
http://www.iata.org/whatwedo/cargo/dgr/Documents/packing-instruction-650-DGR56-en.pdf
Government website
A guide to the international regulations on the transportation of dangerous goods by air, sea, road, rail or inland waterway
International Civil Aviation Organisation (ICAO)
Technical Instructions for the Safe Transport of Dangerous Goods by Air
http://www.icao.int/publications/Documents/
guidance_doc_infectious_substances.pdf
Department for Transport, HSE, Maritime and Coastguard Agency and Civil Aviation Authority
Transport of infectious substances UN2814, UN2900 and UN3373
https://assets.publishing.service.gov.uk/government/uploads/system/
uploads/attachment_data/file/527069/dangerous-goods-guidance-note-17.pdf
World Health Organisation
Transport of Infectious Substances
http://www.who.int/ihr/publications/who_hse_ihr_20100801_
en.pdf?ua=1
Royal Mail
IATA Guidance Document Infectious Substances
http://www.royalmail.com/sites/default/files/Guidance-Document-Infectious-Substances-171012.pdf
You can also refer to your courier's website for advice.