- An SLI is your written instruction to the freight forwarder: it tells them how to ship the goods and authorises them to file the UK export declaration on your behalf.
- It is not legally required in the UK, but almost every forwarder asks for one because it transfers the shipment details and the authority to act as your customs representative in writing.
- A complete SLI carries the exporter and consignee details, your GB EORI number, the goods description and commodity code, value, Incoterms, weights, packages, routing and a signed authorisation.
- It is different from the commercial invoice (proof of sale) and the packing list (what is physically in each box), you usually send all three together.
- Get the commodity code and customs value right: errors flow straight into the customs declaration and can cause delays, duty disputes or penalties.
What is a Shipper's Letter of Instruction?
A Shipper's Letter of Instruction (SLI) is a document the exporter, the "shipper", gives to a freight forwarder or carrier. It does two jobs at once:
- It hands over every detail the forwarder needs to move the goods: who is sending, who is receiving, what the goods are, their value, weight, packaging, and how you want them routed.
- It authorises the forwarder to act on your behalf with customs, specifically, to submit the export declaration to HMRC's Customs Declaration Service (CDS) as your representative.
Think of it as the single instruction sheet that turns "I have a parcel to export" into "the forwarder has everything they need to ship it and clear it." Without an SLI, the forwarder is guessing at details or chasing you by email, which is exactly when mistakes and delays creep in.
The term comes from international freight practice and is used worldwide. In the United States the SLI is closely tied to the Electronic Export Information (EEI) filing; in the UK its main role is to provide the data and the authority for the CDS export declaration.
Is an SLI legally required in the UK?
No. There is no UK law that says you must produce a Shipper's Letter of Instruction. What the law does require is an accurate export declaration for goods leaving Great Britain, submitted through CDS (see HMRC's guidance on making an export declaration).
The SLI is the practical mechanism that makes that declaration happen correctly when a forwarder files it for you. In practice:
- Most freight forwarders will refuse to ship until they have an SLI (or their own equivalent booking form), because it is their written evidence of your instructions and your authorisation to represent you.
- It protects you, too: if the declaration is later questioned, the SLI is your record of exactly what you instructed and the data you supplied.
So while it is not a statutory document, treating it as optional is a mistake. It is the cleanest way to control what gets declared in your name.
What a Shipper's Letter of Instruction must contain
A complete SLI gives the forwarder everything needed for both the physical shipment and the customs declaration. The essential fields:
- Exporter (shipper) details, your legal business name, address, and contact.
- Your GB EORI number, required to export from Great Britain. If you do not have one, see our EORI number guide.
- Consignee details, the receiving party's name and address (and their EORI/tax ID in the destination country where relevant).
- Goods description, a plain, accurate description of what is being shipped (not just "samples" or "parts").
- Commodity code, the 8-digit UK export commodity code for each product line. See our HS / commodity code guide for how to find it.
- Customs value and currency, the value of the goods for customs purposes.
- Incoterms rule, for example EXW, FCA, DAP or DDP, which sets who is responsible for what along the journey.
- Weights and packaging, gross weight, net weight, number and type of packages.
- Routing and carrier preferences, origin, destination, mode (air/sea/road), and any preferred carrier or service level.
- Export licence / controlled-goods notes, flag anything that needs a licence (dual-use items, certain chemicals, etc.).
- Authorisation statement and signature, appointing the forwarder as your direct or indirect representative for the customs declaration.
Shipper's Letter of Instruction template (field by field)
Copy the structure below into a document or your forwarder's portal. Every field maps to something the forwarder needs to ship and declare your goods.
| Section | Fields to complete |
|---|---|
| 1. Exporter / shipper | Legal name · address · contact name, email, phone · GB EORI number · VAT number (if applicable) |
| 2. Consignee | Name · full delivery address · destination country · tax/EORI ID · contact |
| 3. Notify party | (If different from consignee) name and contact for arrival notifications |
| 4. Forwarder / carrier | Appointed forwarder name · account/booking reference · preferred service |
| 5. Goods | Per line: description · commodity code · quantity · unit value · line value · country of origin |
| 6. Value & terms | Total customs value · currency · Incoterms rule + named place |
| 7. Logistics | Gross weight · net weight · number of packages · package type · dimensions · mode of transport |
| 8. Compliance | Export licence reference (if any) · controlled/dual-use flag · special handling (hazmat, temperature) |
| 9. Authorisation | Representation type (direct / indirect) · authorised signatory name · signature · date |
SLI vs commercial invoice vs packing list
These three documents travel together but do different jobs. Mixing them up is the most common cause of confusion for new exporters.
| Document | Purpose | Who it is for |
|---|---|---|
| Shipper's Letter of Instruction | Instructs the forwarder how to ship and authorises them to file the export declaration | Your freight forwarder / carrier |
| Commercial invoice | Evidences the sale and the value of the goods; used by customs to assess duty and VAT in the destination country | Customs (both ends) and the buyer |
| Packing list | Itemises what is physically in each box/pallet: quantities, weights, dimensions | Warehouse, carrier and customs inspection |
In short: the SLI is your instruction to the forwarder, the commercial invoice is proof of the sale, and the packing list describes the physical contents. The SLI references information that also appears on the invoice (value, goods description) but is not a substitute for it.
Direct vs indirect representation
When you authorise a forwarder to file the customs declaration, you appoint them as your representative in one of two ways. The SLI should state which.
- Direct representation, the forwarder acts in your name and on your behalf. You remain solely liable for the accuracy of the declaration and any customs debt. This is the usual arrangement for established UK exporters.
- Indirect representation, the forwarder acts in their own name but on your behalf, and becomes jointly and severally liable with you for the customs debt. Forwarders are more cautious about offering this and may charge more.
HMRC explains the distinction in its guidance on appointing someone to deal with customs on your behalf. If you are unsure which you are agreeing to, ask the forwarder to confirm in writing, it changes who carries the liability if something is wrong.
Common SLI mistakes (and how to avoid them)
- Vague goods descriptions. "Parts" or "samples" invites customs queries. Describe what the item actually is, what it is made of, and what it is used for.
- Wrong or missing commodity code. The code drives duty and controls in the destination country. Look it up properly, see our HS code guide, rather than reusing a code from an unrelated product.
- Under- or over-stating value. The customs value must be accurate. Understating to reduce the buyer's duty is a customs offence; overstating inflates their duty and VAT unnecessarily.
- No EORI, or the wrong one. You need a GB EORI to export from Great Britain. Northern Ireland movements may need an XI EORI. See the EORI guide.
- Leaving the Incoterm blank. Without an agreed Incoterms rule, it is unclear who pays freight, insurance and import charges, a frequent source of disputes with overseas buyers.
- Not specifying representation type. Always state direct or indirect so liability is clear.