Using the Trader Support Service for GB-NI Movements: What Businesses Get Wrong

Many businesses assume that using the Trader Support Service (TSS) means their customs management is covered. They are not.

The TSS submits declarations using the data you provide. If that data is wrong, the customs declaration is wrong (and the liability sits with you, not the service).

That gap between what the TSS handles and what businesses assume it handles is where most delays, rejected declarations, and compliance exposures come from. This guide sets out what the common problems are, who is responsible for what and how to build a process that holds up under scrutiny.

What the Trader Support Service actually does

The Trader Support Service is a free-to-use service funded by the UK government, designed to support businesses with the UK customs requirements for GB-NI movements. It was built to help traders meet the UK customs requirements introduced under the Northern Ireland Protocol, now succeeded by the Windsor Framework.

It operates across two main channels:

1. You can access guidance, training and support through the TSS portal and helpline.
2. You can also authorise the TSS to submit customs declarations on your behalf through a simplified customs declaration

Under that simplified approach, the TSS can submit the initial frontier declaration at the point of movement. Depending on the goods and their risk profile, a supplementary declaration may also be required within a set period. That supplementary declaration carries the full customs detail and remains your legal responsibility, whether TSS submits it or not.

The TSS reduces the operational barrier to entry. It does not remove your underlying compliance obligations.

The Windsor Framework and what it means for GB-NI movements

The Windsor Framework, which replaced the Northern Ireland Protocol, introduced a more structured approach to goods moving from Great Britain to Northern Ireland.

Goods destined to remain in Northern Ireland for sale or use follow the UK Internal Market Scheme (UKIMS), which simplifies the UK customs requirements for qualifying businesses and goods. Goods that are at risk of moving into the EU face a different set of requirements, including standard customs management duties.

For most retailers, manufacturers and logistics providers, UKIMS authorisation is the route to simpler, lower-cost movement. The Trader Support Service supports UKIMS declarations and can help businesses understand whether they qualify.

The key is not to assume eligibility. UKIMS has its own application criteria, and the goods themselves must meet the conditions for the simplified treatment to apply. Claiming UKIMS treatment for ineligible goods, or failing to apply for authorisation at all, can create both delays and unexpected duty liability.

The most common Trader Support Service challenges

Most problems with the TSS fall into the same areas, regardless of business size or sector:

• Data quality. The TSS can only submit declarations using the information you provide. Incorrect commodity codes, missing origin data, incomplete invoice details, inaccurate values or inconsistent product descriptions all cause delays or rejections. For businesses with large product catalogues or fragmented systems, this is where problems most often start.
• Supplementary declaration workload. The TSS facilitates movements, but ongoing obligations around supplementary declarations, record keeping and audit readiness remain with you. Deadlines are strict, customs declaration errors can trigger amendments, and missing data causes submission failures. If you’re a higher-volume trader, you may find that manual processes become unmanageable quickly.
• Understanding which rules apply. The Windsor Framework introduced different processes depending on whether goods are at risk of entering the EU, whether they qualify for green lane arrangements, what type of goods are being moved and whether you hold UKIMS authorisation. If your supply chains change frequently, this will be harder to manage consistently.
• Manual data processing. Moving information between ERP systems, spreadsheets, freight systems, warehouse platforms and the TSS portal creates multiple points of failure. Declaration rejections, mismatched records and shipment delays are common consequences.
• Scaling. The TSS can work reasonably well at lower volumes. As your customs declaration volumes grow, the process becomes operationally heavy. Retailers, wholesalers, food importers and third-party logistics (3PL) providers tend to feel this most acutely, because the challenge shifts from basic compliance to building repeatable, scalable customs workflows.

Practical steps to strengthen your customs management

Most delays in GB-NI movements are preventable at the data level. These steps apply whether you’re using the Trader Support Service directly or alongside other arrangements.

• Build and maintain a controlled item master. For every product involved in GB-NI movements, you need a verified commodity code, a defensible customs valuation method and a confirmed country of origin. Treat it as a live document, not a spreadsheet built once and forgotten.
• Assign clear ownership for declaration data. Someone in your business needs to own the accuracy of the data that feeds customs declarations, and that responsibility needs to cover a process for handling changes, from new products and suppliers to revised commercial terms.
• Understand your supplementary declaration obligations. Where a supplementary declaration is required, it carries the legal weight of the customs entry. If you’re using the TSS to submit frontier declarations, confirm in advance which movements will also require a supplementary declaration and who is responsible for submitting it.
• Check UKIMS eligibility. If your goods qualify and you’re not yet authorised, applying reduces friction significantly. If you’re already authorised, make sure your customs declarations consistently reflect the correct treatment for each product.
• Keep documentation accessible. Organise commercial invoices, packing lists, proof of origin and supporting documents by shipment so they can be retrieved quickly.

When to go beyond the Trader Support Service

The Trader Support Service works for many businesses at lower volumes and in the earlier stages of getting GB-NI movements under control. It was not designed to carry the full weight of your customs operations as those operations grow.

The TSS does not create or maintain the audit trails that supplementary declarations need, and it will not prepare you for an HMRC audit. Authorisations such as the Simplified Customs Declaration Process (SCDP) need active governance that the TSS was never designed to provide.

Many businesses that adopted the TSS quickly after Brexit are still running on the same setup years later. If that sounds familiar, there are three practical routes forward.

• Bring your declarations in-house using customs declaration software built for the Customs Declaration Service (CDS). Purpose-built customs duty management systems give you direct control over submissions, built-in validation and clear audit reporting, which is particularly useful when you’re managing supplementary declarations at volume. Langdon’s DMS Lite is built specifically for importing supplementary declarations and customs warehouse removals submitted to HMRC CDS.
• Outsource to an expert team with documented customs management This route is ideal if you need more control and compliance assurance than the TSS provides, without the overhead of building an in-house function. Langdon’s Bureau team acts as an outsourced customs function, handling your customs declarations end to end with clear escalation routes and full audit trails.
• Get consultancy support to address authorisations, audit readiness or compliance gaps. Specialists who know GB-NI trade will identify and close the gaps faster than working through them internally. Langdon’s Consultancy service supports businesses through HMRC authorisations, as well as compliance reviews and process improvement.

An HMRC audit or a retrospective duty liability bill is not the moment to find out your GB-NI process has gaps. Speak to our team today at info@langdoncustoms.com to reduce your compliance risk.