Managing Director, HC-Customs Limited · Customs compliance specialist · Brexit formalities · Updated January 2026
MRN
Movement Reference Number — unique ID for each declaration
4 years
Record retention requirement under HMRC Notice 143
6 fields
Core data points to reconcile per declaration
100%
Of HMRC audits request CDS reconciliation records
What is CDS and why does reconciliation matter?
The Customs Declaration Service (CDS) replaced CHIEF (Customs Handling of Import and Export Freight) as HMRC's core customs IT platform from November 2023. All UK import and export declarations are now processed through CDS, and every declaration is stored under the importer's EORI number.
CDS reconciliation is the process of comparing what HMRC holds on CDS — the declared customs value, commodity code, duty paid, procedure, and origin — against what you actually instructed your customs agent to declare, and what you paid your supplier.
The gap between your internal records and what appears on CDS is your compliance risk. A discrepancy that goes undetected for months creates a growing liability — because HMRC can assess for up to 4 years, and each new declaration where the same error repeats compounds the amount potentially owed.
How to access your CDS data
Option 1 — Live CDS API via OAuth2 (recommended)
HMRC provides the Customs Declarations Information (CDI) API, which allows authorised software to pull live declaration data directly from CDS in real time. Accessing CDI requires registering an application on the HMRC Developer Hub and completing OAuth2 authorisation with a Government Gateway account enrolled for your EORI.
HC Customs provides a built-in CDS connection via OAuth2 — connect once and your declarations sync automatically, with new MRNs appearing within minutes of HMRC acceptance.
Option 2 — HMRC TRE (Trade Reporting & Extracting)
HMRC's free TRE service provides a downloadable CSV of your full import history — covering both CHIEF and CDS data going back years. TRE is accessible via Government Gateway and delivers a data file within 48 hours of request. It replaced the paid CDS MSS (Management Support System) from April 2026.
HC Customs can ingest a TRE CSV directly — upload it and the platform maps all declarations into the reconciliation dashboard automatically. See the HMRC TRE guide for step-by-step instructions.
6 discrepancies CDS reconciliation catches
Customs value mismatch
The value declared on the MRN differs from your commercial invoice. This can result in either overpaid or underpaid duty — both create a liability.
Commodity code discrepancy
Your CCI instructed a different commodity code than what your agent filed. Even a subheading difference (10-digit level) can mean a different duty rate.
Origin claim not reflected
You provided proof of origin to your agent but the declaration shows MFN duty was applied. The preference was not claimed — overpayment opportunity.
Procedure code error
Wrong procedure code (e.g. 40 00 vs 51 00) can affect whether goods entered IP, returned goods relief, or standard import — with significant duty implications.
PVA not recorded correctly
Postponed VAT Accounting was elected but the import VAT appears on the C79 certificate with the wrong EORI or period — causing VAT reconciliation to fail.
Missing declaration
A shipment you paid for does not appear in your CDS data — suggesting either a misfiled EORI, an unreported consignment, or a customs agent error.
The CDS reconciliation process — step by step
Step 1 — Pull your CDS data
Connect to CDS via OAuth2 (live) or download your TRE export. You need a complete list of all MRNs accepted under your EORI for the reconciliation period, along with the key declaration fields: commodity code, declared customs value, duty paid, procedure code, origin country, and preference status.
Step 2 — Match against your Customs Clearance Instructions (CCIs)
For each MRN, compare what HMRC accepted against the Customs Clearance Instruction you issued to your agent before the shipment. The CCI is your authoritative record of what you instructed — it establishes whether a discrepancy was an agent error (creating a correction claim) or your own error (creating a voluntary disclosure obligation).
Step 3 — Match against supplier invoices
Verify the declared customs value for each MRN against your purchase order, commercial invoice, and payment records. Remember: customs value is CIF (Cost + Insurance + Freight to the UK border), not just the invoice value. Common errors include excluding insurance, using a FOB value for a CIF declaration, or double-counting freight.
Step 4 — Reconcile C79 and PVA statements
Your monthly C79 certificate (physical import VAT) or PVA statement (postponed VAT accounting) must reconcile against your CDS declarations for the same period. A mismatch between the two means either an MRN is missing from CDS, the wrong EORI was used, or a PVA election was not processed correctly — all of which create a VAT compliance issue.
Step 5 — Flag and action discrepancies
Each discrepancy identified falls into one of three categories: (a) recoverable overpayment — file C285; (b) underpayment you need to voluntarily disclose — submit a voluntary disclosure before HMRC contacts you; (c) data quality error — correct your internal records. Maintaining a reconciliation log of discrepancies found and actioned is itself valuable audit evidence.
What a reconciled declaration looks like
MRN 26GB555000000001X4
Accepted 14 May 2026 · Commodity 8483 40 51
HC Customs Platform
Automated CDS reconciliation — every MRN, every month
HC Customs connects to HMRC CDS directly via OAuth2, pulls your declarations automatically, and reconciles each MRN against your CCIs and uploaded invoices. Discrepancies are flagged with a one-click action — file C285, raise voluntary disclosure, or update internal records.
Frequently asked questions
What is an MRN and where do I find it?
An MRN (Movement Reference Number) is the unique 18-character reference assigned by HMRC CDS when an import declaration is accepted. Format: YYGB + EORI digits + sequential reference + check digit. Your customs agent should provide MRNs for every shipment. You can also retrieve them directly from CDS via the CDI API or from your TRE export.
How often should I run a CDS reconciliation?
For businesses importing regularly, monthly reconciliation is best practice and aligns with your PVA/C79 statement cycle. At a minimum, run a full reconciliation annually. If you are under HMRC audit, you will need to produce reconciliation evidence for the specific period under review.
What is the difference between CDS reconciliation and a CDS MSS?
CDS MSS (Management Support System) was a paid HMRC data feed that provided daily declaration data. It was replaced by the free TRE service in April 2026. CDS reconciliation is the process — MSS/TRE are the data sources. Live CDI API access, as provided through HC Customs, is the most current and real-time alternative.
What if my customs agent won't provide MRNs?
As the importer of record, you have a legal right to the MRNs for all declarations made under your EORI. If your agent refuses to share them, you can access your own CDS data via Government Gateway (through TRE) without needing the agent's cooperation. This is also a good reason to consider changing agents.