Where do I enter the chemical CUS code in an import declaration?

The CUS number is the identification number assigned to chemical products in the European Customs Inventory of Chemical Substances (ECICS) database.

To enter this value, open the item and locate the Commodity code section on the Item tab.  

You should refer to data element 6/13 of the tariff for information on entering this code.

Useful links:

https://www.gov.uk/government/publications/cds-uk-trade-tariff-volume-3-import-declaration-completion-guide/group-6-goods-identification#data-element-6-13

https://taxation-customs.ec.europa.eu/online-services/online-services-and-databases-customs/ecics-european-customs-inventory-chemical-substances_en