What Is an LRN? LRN Number, Format and Difference from MRN and DUCR

LRN stands for Local Reference Number: the reference number a declarant gives a customs declaration or transit declaration before the customs system issues the official MRN. It is not issued by customs. You (or your customs agent) create it, so you can find the declaration in your own records. In the UK’s CDS it goes in data element DE 2/5, is up to 22 alphanumeric characters and must not be reused by the same trader within 48 hours.

The MRN, by contrast, is allocated only by the system: in CDS once the declaration is submitted, in NCTS transit once the declaration is accepted.

Below we explain how an LRN differs from an MRN and a DUCR, who creates it, what it looks like in CDS, in NCTS transit and in EU declarations, and where you enter it. Every fact rests on GOV.UK, EU regulations or the Polish PUESC instruction.

What is an LRN?

An LRN is the number with which the declarant labels its own declaration before the customs authority or system assigns an official number. Delegated Regulation (EU) 2015/2446 describes it in Annex B (data element 12 09 000 000, formerly 2/5): the LRN is “nationally defined and allocated by the declarant in agreement with the competent authorities to identify each single declaration” (Regulation (EU) 2015/2446, consolidated text). The format in the EU data tables is an..22, that is up to 22 alphanumeric characters (Implementing Regulation (EU) 2015/2447, Annex B, consolidated text). The PUESC instruction describes the LRN as the local record number of the consignment (PUESC: Transit instruction for NCTS2 PLUS).

In practice the LRN is your own label for finding the declaration in your own system. It is not proof that customs accepted the declaration, and the onward movement of the goods (for example at the offices of transit and destination) relies on the MRN, not the LRN.

What does LRN mean in customs, and what does an LRN number look like?

When people search for “LRN customs” or “LRN reference number”, they usually mean the field labelled Local Reference Number on a customs declaration. There is no government-issued LRN to look up: the LRN number is whatever unique reference the declarant chooses within the limits of the system. In CDS the only format rule is an..22 (up to 22 alphanumeric characters); GOV.UK requires it to be unique to the transaction and to the submitting trader (CDS Volume 3, Group 2). The EU data requirements use the same an..22 format for the LRN.

A practical way to build one is a prefix of your own, the date and a running number, for example the pattern in the illustrative example below. Whatever scheme you choose, keep it within 22 characters and never repeat it.

1. Who creates it: the declarant, or the agent submitting on the declarant’s behalf.
2. When: before or at the moment the declaration is submitted.
3. What to keep: note the LRN next to the invoice and transport references, so you can match it later with the MRN the system returns.

LRN, MRN and DUCR: the differences

Sources for the table: the HMRC CDS glossary, CDS Volume 3 (imports), Group 2 and CDS Volume 3 (exports), Group 2. A longer comparison of all three numbers is in MRN, DUCR and LRN, and the MRN is covered in MRN: movement reference number for customs clearance.

The LRN in CDS (United Kingdom)

In the CDS declaration completion instructions (UK Trade Tariff, Volume 3) the LRN is data element DE 2/5. The same rules apply to imports and exports (GOV.UK: imports, GOV.UK: exports):

• Mandatory: the declarant must enter a reference number for each transaction.
• Format: an..22, one occurrence at header level (not at item level).
• Uniqueness: the number must be unique to the transaction, unique within a 48-hour period and unique for the submitting trader.
• Duplicates: declarations submitted within a 48-hour period by a user identity with a duplicate LRN are rejected.

Note the difference in how the window is described: the HMRC CDS glossary says the LRN must be unique for 2 days from acceptance of the declaration. So in practice never reuse an LRN; build it on a scheme that does not repeat (for example a date plus a running number).

In CDS the MRN is allocated by the system. The HMRC glossary describes the MRN as a globally unique identifier for a declaration and says CDS assigns it after the declaration is submitted. It is the MRN, not the LRN, that you use later to refer to a specific declaration, for example as the previous document in a supplementary declaration (code “SDE” followed by the simplified declaration MRN in DE 2/1). Changes to the system itself are covered in Changes to CDS.

DUCR: how it differs from the LRN

The DUCR (Declaration Unique Consignment Reference) is assigned by the declarant to uniquely identify a single consignment of goods; it can relate to more than one customs declaration (HMRC glossary). On exports from Great Britain it is declared in DE 2/1 with document code DCR and is mandatory for all declarations. HMRC’s recommended DUCR format (the WCO format) has five parts: a single digit for the year (for 2025 this is “5”), the country code (GB or XI), the EORI number, a dash, and a trader-devised reference (CDS Volume 3, exports). For imports, a DUCR is required, among other cases, for the simplified declaration procedure and entry in the declarant’s records (EIDR), in DE 2/1 with code “DCR”.

The LRN in NCTS transit

In Poland’s NCTS2 PLUS the declarant sends message IE015 (transit declaration). If it is technically and formally correct, it receives IE928 (confirmation that the declaration data has been saved in the system), and at that stage the declaration is identified by the LRN. Only message IE028 confirms acceptance of the declaration and the allocation of the MRN (PUESC, instruction version 1.03).

For an advance declaration (value “D” in the “additional declaration type” element), submitted up to 30 days before the goods are presented, the declarant should send IE170 within 30 days after IE928 (information on presentation of the goods). It then receives IE028 with the MRN. If IE170 does not arrive in that period, the declaration is rejected (IE056). This shows why the LRN is not enough: IE928 alone does not mean the declaration was accepted.

The onward movement of the goods relies on the MRN: under Articles 304 and 306 of Regulation 2015/2447, goods are presented at the customs office of transit and at the customs office of destination together with the MRN of the transit declaration (Regulation (EU) 2015/2447). When the business continuity procedure (BCP) is used, no MRN is allocated (GOV.UK: Transit Manual Supplement, chapter 7). The transit procedure is explained in How does T1 transit work?.

LRN, T1 and GMR: how the numbers connect on a UK–EU journey

A T1 transit document is the paperwork behind a transit declaration; the declaration itself carries an LRN while you prepare it and an MRN once it is accepted. The LRN does not travel with the goods. If a haulier needs a Goods Movement Reference (GMR), the GMR is a separate reference, and GOV.UK asks you to include declaration references in it: depending on the route, that is an MRN generated by NCTS or the Transit Accompanying Document (TAD) MRN for goods moving under the Common Transit Convention, or the DUCRs of the export declarations (for example combined customs and safety and security export declarations from Great Britain to the EU) (GOV.UK: Get a goods movement reference). In short: use the LRN for your own tracking, and the MRN or DUCR where an official reference is asked for.

The LRN in EU declarations

In EU law the LRN is data element 12 09 000 000 (formerly 2/5) in Annex B to Delegated Regulation 2015/2446 and in Annex B to Implementing Regulation 2015/2447 (format an..22). Under Article 226 of Regulation 2015/2447, customs notify the declarant of the acceptance of the customs declaration and provide an MRN for it together with the date of acceptance (Article 226). It works similarly for the entry summary declaration (ENS): the customs authorities register it, immediately notify the person who lodged it and communicate the MRN and the date of registration (Article 185).

Common LRN mistakes

• Reusing an LRN. In CDS a duplicate within 48 hours leads to the declaration being rejected.
• Giving the LRN instead of the MRN. At the customs office of transit and at destination you present the MRN of the transit declaration, not your working number.
• Treating the LRN as proof of acceptance. In NCTS, confirmation that the data was saved (IE928) is not acceptance; acceptance is confirmed by IE028 with the MRN.
• An LRN that is too long or in the wrong format. The format is a maximum of 22 alphanumeric characters.
• Confusing the LRN with the DUCR. A DUCR has a recommended structure (year, country, EORI, dash, reference) and relates to a consignment.

Example (illustrative)

A UK exporter sends goods to Poland and an agent submits the export declaration in CDS. The declaration gets an LRN on the pattern “EC20261024017” (13 characters, a date plus a running number, so it will not repeat within 48 hours). The DUCR looks like “6GB123456789000-EC0017”: 6 stands for 2026, GB for the country, and GB123456789000 is a fictitious EORI number. Once the declaration is submitted, CDS allocates the MRN, which identifies the declaration in the onward process, while the LRN remains the declarant’s working number.

When a customs agent helps

We are a customs agency registered in CDS with a UK EORI number. We assign and monitor references in import, export and transit declarations to avoid rejections. See customs clearance from the UK. Costs are on one page only: how much does UK customs clearance cost.

Frequently asked questions