Trading between Great Britain (GB) and Northern Ireland (NI) involves specific customs requirements. For many businesses using simplified import processes through the Trader Support Service (TSS), a key obligation is the submission of a post-import supplementary declaration.
Smart Customs helps businesses trading between GB and NI manage TSS supplementary declarations without the risk, delays, or administrative burden. As an authorised TSS agent, we can complete supplementary declarations on your behalf, take over existing TSS records where required, and resolve outstanding or overdue submissions to keep your NI trade compliant and uninterrupted.
What is a Northern Ireland Supplementary Declaration?
A Northern Ireland supplementary declaration is a post-import customs declaration submitted after goods have arrived in Northern Ireland. It provides the full customs dataset that was not required at the time of entry under simplified procedures.
Where traders use an initial simplified declaration or Entry in Declarant’s Records (EIDR), the supplementary declaration completes the customs process by confirming:
• Commodity codes and accurate product descriptions
• Customs value and valuation method
• Origin details
• Customs procedure codes
• Any applicable duty, VAT, or reliefs
These declarations are a legal requirement where the movement has not been completed through an alternative Internal Market process.
TSS Supplementary Declarations Explained
The Trader Support Service (TSS) supports businesses moving goods into Northern Ireland by enabling simplified frontier processes. However, TSS does not remove the obligation to submit supplementary declarations where they apply.
A supplementary declaration may be required when:
• Goods move from Great Britain to Northern Ireland
• A simplified or EIDR process is used at import
• Full customs data was not provided at the point of entry
• The movement has not been completed through an Internal Market Movement (IMMI) process
While TSS provides the platform, the accuracy of the declaration remains the trader’s responsibility. Errors or omissions can trigger compliance checks or follow-up queries from HMRC.
When Are NI Supplementary Declarations Required?
You will typically need to submit a Northern Ireland supplementary declaration if you are:
• Importing goods from GB to NI under simplified procedures
• Deferring full customs data at the time of import
• Moving controlled, restricted, or higher-risk goods
• Not eligible for IMMI conversion or Green Lane simplifications
Under the Windsor Framework, some qualifying movements (for authorised UKIMS traders) may instead be converted to IMMI records, reducing the need for full supplementary declarations.
Deadlines are strict, and late submissions can lead to enforcement action even where no duty is ultimately payable.
NI Supplementary Declarations and “At Risk” vs “Not At Risk” Goods
Under the Windsor Framework, goods moving from Great Britain into Northern Ireland may be treated as either “at risk” or “not at risk”, depending on their final destination and whether the trader holds the relevant authorisations (such as UKIMS).
This classification can affect:
• whether customs duty may arise, and
• how the movement is processed within HMRC systems.
It’s important to note that supplementary declarations may still be required even where goods are ultimately not subject to duty, depending on:
• how the original frontier entry was made,
• whether simplified procedures or EIDR were used, and
• whether the movement qualifies for conversion to an Internal Market Movement (IMMI) record.
Smart Customs can help ensure the correct procedures and indicators are applied, reducing the risk of unnecessary follow-up requirements or overdue declarations.
Common Challenges with TSS Declarations
Many businesses find NI supplementary declarations more complex than expected. Common problem areas include:
• Incorrect commodity codes or valuation
• Misunderstanding customs procedure codes
• Incomplete origin evidence
• Difficulty matching invoices to customs data
• Managing large volumes of declarations
• Backlogs of overdue supplementaries triggered automatically by the system
Because supplementary declarations are submitted after goods have moved, issues are often discovered only after arrival, increasing compliance and commercial risk.
FAQ
How to Complete Northern Ireland Supplementary Declarations
To complete a supplementary declaration correctly, traders must:
• Collect full commercial documentation
• Classify goods correctly using the UK tariff
• Confirm origin and valuation methodology
• Apply the correct customs procedure codes
• Submit within the required timeframe via TSS or another customs system
For many businesses, especially those with frequent GB to NI movements, this becomes time-consuming and resource-heavy.
Outsourcing TSS Supplementary Declarations
Outsourcing Northern Ireland supplementary declarations is increasingly common, particularly for businesses that:
• Import regularly into Northern Ireland
• Lack in-house customs expertise
• Want to reduce compliance risk
• Need consistent, audit-ready submissions
• Have overdue supplementaries raised by HMRC/TSS
A specialist customs agent can manage the full process, ensuring submissions are accurate and aligned with current HMRC and Windsor Framework requirements.
TSS Supplementary Declarations – How We Support You
Smart Customs holds an authorised agent account within the Trader Support Service,
allowing us to submit Northern Ireland supplementary declarations directly for your business.
Where required, we can also:
• Take over existing TSS records
• Review previous submissions
• Complete outstanding or overdue declarations
• Advise on IMMI conversion eligibility and correct UKIMS usage
This approach is particularly useful for businesses that:
• Do not have the time or expertise to manage TSS submissions
• Have accumulated outstanding supplementary declarations
• Want reassurance that declarations are compliant and audit-ready
By handling the full supplementary declaration process, we help ensure your GB to Northern Ireland movements remain compliant without disrupting your day-to-day operations.
