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A certification of origin states the claim. A defensible origin file is the evidence that lets the claim survive a verification.
When you import a UK-origin good under the TIPAT (the CPTPP), the certification of origin is what you hand over to claim the preferential rate. The origin file is what you keep, and it is what decides the outcome if the Servicio de Administración Tributaria (SAT) verifies the claim months or years later. Operations regularly get the first part right and the second part wrong: a clean certification on the entry, and nothing behind it when the verification letter arrives.
This playbook is for the operator who has to qualify a UK good under the TIPAT and build a file that holds up. By the end you will know how to read the product-specific rule for your tariff classification, how to run the cumulation analysis the TIPAT now allows, who should sign the certification, and exactly which records to keep so the preference is defensible. For the broader picture of what the TIPAT changed for UK goods, see what decides zero duty versus full tariff.
Before you start: what you need for a TIPAT origin analysis
Have four things in hand. The correct tariff classification of the good, down to the level the rules of origin operate on. A complete bill of materials, listing every input with its own classification and country of origin. The origin status and supporting evidence for each input, originating in a TIPAT country or otherwise. And the product-specific rule of origin that applies to your good, from Annex 3-D of the TIPAT.
Decide one thing up front: who will certify. Under the TIPAT, the certification of origin can be completed by the exporter, the producer, or the importer (Article 3.20). That choice changes who holds the documentary burden, and it is easier to make before you build the file.
Step 1. Classify the good correctly
Origin analysis depends entirely on classification. The product-specific rule of origin is keyed to the good's tariff classification, and many rules turn on a change in classification from the inputs to the finished good. If the classification is wrong, every step after it is wrong, and the file rests on a false foundation.
Classify the finished good and every material in the bill of materials. A change-in-classification rule can only be tested when the classification of each input is known alongside the product's.
Step 2. Read the product-specific rule of origin for your tariff classification
Go to Annex 3-D and find the rule for your good's classification. TIPAT product-specific rules take one of a few forms, and you need to know which one yours is.
A change in tariff classification (CTC) rule requires the non-originating inputs to transform into the finished good across a defined classification boundary. A regional value content (RVC) rule requires a minimum percentage of value to originate in the TIPAT region, calculated by one of the methods the agreement defines. Some goods carry a specific process rule. Read the rule literally, then check whether your good meets it as built.
If your good misses a change-in-classification rule only because of a small share of non-originating material, the de minimis provision (Article 3.11) may still let it qualify. Confirm the exact threshold and apply it precisely. It works as a safety valve on top of a complete analysis.
On the entry, the question is whether the good carries a certification. Under a verification, the authority examines the file behind it. The gap between those two documents is where preferences are lost.
Step 3. Run the TIPAT cumulation analysis
This is the lever the TIPAT added to the old bilateral framework. Under Article 3.10, materials and production from any of the twelve TIPAT economies can count toward whether your good originates. A UK good built partly from Japanese, Canadian, or Vietnamese inputs can now count those inputs, where the prior Mexico-UK framework would have treated them as non-originating.
Map each input in the bill of materials to its origin, and identify which ones are originating in a TIPAT country. Regional cumulation can be the difference between a good that fails the rule and one that clears it. It is also the part of the analysis most likely to need documentation from your supplier's supplier, so start it early.
Step 4. Decide who certifies, and accept the burden that comes with it
The certification of origin has no mandatory format. It must carry the minimum data elements in Annex 3-B and identify whether the certifier is the exporter, the producer, or the importer (Article 3.20). In Mexico, importer self-certification has been available since the Reglas Generales de Comercio Exterior reform that took effect on December 29, 2023, so certifying as the importer is a practical option.
Choose deliberately. If the producer or exporter certifies, they hold the origin evidence, and your contract should oblige them to cooperate in any verification and to keep the records. If you certify as the importer, the documentary burden is yours, and you must hold the information that supports the claim at the time you make it (Article 3.24). For a good whose production data sits outside your control, importer certification is powerful and heavy. For a good you build, or whose supply chain you can document, it can be the cleaner path.
Step 5. Build the origin file that survives a SAT verification
This is the step the title is about. A defensible origin file assembles, for each good and each period the certification covers: the tariff classification analysis for the finished good and the inputs; the complete bill of materials with origin status per input; the product-specific rule applied and the worked analysis showing the good meets it (the CTC mapping or the RVC calculation); the supplier origin evidence for originating inputs and the de minimis calculation for any non-originating ones; and the certification of origin itself with the Annex 3-B elements.
Keep all of it for at least five years from the date of importation (Article 3.26). The customs authority can verify a claim after the fact through written information requests and verification visits, and the answer to that verification is the file, ready to hand over on the day it is requested.
Common mistake. Certifying a good as originating because "it always qualified" or because the supplier said so, without the bill-of-materials analysis behind it. A supplier's assurance is a starting point for the file. When the verification lands, an unsupported certification converts the duty saving into an assessed underpayment, plus the consequences that attach to a claim that could not be substantiated.
What a finished origin file looks like
A finished file is a certification you could hand to a verifying officer alongside evidence that proves, input by input, why the good originates, for every entry in the period the certification covers. If you can reconstruct the origin determination today without calling the supplier, the file is defensible. If you would need that call, the file is a liability dressed up as a saving.
When to bring in a customs broker for TIPAT origin
Bring in a customs broker or trade compliance specialist when the product-specific rule is an RVC calculation, when cumulation across multiple TIPAT countries is what makes the good qualify, or when you are setting up a UK lane and want certainty before the first entry. If the good also falls under a quota, our guide to TIPAT import quotas and the certificado de cupo covers that second requirement. The TIPAT also preserves the option to request a resolución anticipada (an advance ruling) on origin from the authority, which converts a judgment call into a documented determination before the cargo moves.
Across more than 190,000 customs operations a year at 39+ ports, the origin claims that fail a verification are usually the ones where the good qualified and nobody kept the proof. The certification states the claim, and the file shows it was true. Build the file first, and the certification takes care of itself. Mexican exporters shipping the other way face the same discipline, covered in what the UK's TIPAT accession opens for Mexican exporters.
Talk to a Joffroy expert about an origin-file review for your UK-origin goods under the TIPAT before your first entries clear.
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