CDS Data Element 2/3

What is the difference between 'union' codes and 'national' codes in CDS data element 2/3 - and how do you decide which one is appropriate?

Hi,
For the specific movement types, requires users to identify in DE 2/3 the need for any commercial or official documents, such as invoices, packing lists, licences, certificates or authorisations to be declared on the customs declaration or Customs Clearance Request (CCR). 
Codes which begin with a letter are referred to as Union Codes. These take precedence over any National document codes, they include licences, preference certificates and authorisations.
Codes begin with a number and are referred to as National Document Codes, they are used to declare any national documentary requirements such as home office licences or HMRC forms
Please see below links for more guidance.
CDSSG04710 - Navigating the Tariff, Step 7 - Understanding document codes in CDS
CDSSG04700 - Navigating the Tariff, Step 7 - Document Codes: Contents
Thank you.
 

Thanks - so how do I know which one is required at which time? For example when making a claim to preferential origin. How do I know if I should use U110 or 9001? What does it depend on?

In relation to the two codes you mention it will depend on which trade agreement that the claim is made under and also what proof of preferential origin is presented. So for example U110 would be for a statement on origin for the TCA or JP- UK agreement. 9001 for an origin declaration for DCTS , UK - TR . You may need to use multiple document codes on an entry

Thanks Customs Oldtimer - I still dont feel this explains how you would know to choose U110 or 9001 since the trade agreements do not specify.
Also under what circumstances would you need to use multiple preference codes?

In many cases (but not all for some reason) the details needed for preference are published in the tariff schedule. If you check a hs code, specify an export country and check the origin tab it will say which codes apply .
Example below for Benin
Prove the origin of your goods
You may need provide evidence to prove the preferential origin of your product.
Under the Developing Countries Trading Scheme (DCTS) - Comprehensive Preferences valid proofs of origin include:
Generalised Scheme of Preferences Form A Origin declaration
Declaring your proof of origin CDS Data Element (DE)
What you must include DE 2/3
You must include one of the following document codes, as appropriate:
9001 (origin declaration)
N865 (Form A) DE 4/17
The data element must include a preference code in the 200 series. There isn’t need to use multiple preference codes but there is usually need to use multiple document codes in DE2/3.

Hi LL
Unfortunately, we are unable to offer advice on specific document codes as which ones to use on declarations as they are part of legal information.
You need to read guidance on each document code as per their appendices. If you have issues with declaring a particular code where you receive an error code, you can raise a ticket with CDS team.
Report a problem using the Customs Declaration Service 
Thank you.
 

Thanks, my question is really around how to know whether to use a national or a union code (not specifically which code). This is for importing and claiming preference for any trade agreement on import into the UK. Since the tariff does not specify which ('national or union') should be used and the trade agreement also does not - how do I know if I should apply a national or a union code?

Hi,
To check which document is required to claim preference, you do need to refer to trade tariff UK. Once you searched the commodity and filtered the country, you should be able to see if there is a preference available for customs duty. If a preference exists, it also tells which document code (national/union) can be used to claim the preference: 
Trade Tariff: look up commodity codes, duty and VAT rates
Thank you.