Now underway. HMRC has confirmed the retirement timetable for the current Trader Support Service platform. A new platform goes live on 20 October 2026. Access to the outgoing platform ends on 30 November 2026 — see HMRC’s guidance on GOV.UK.
TSS and the Windsor Framework
Northern Ireland sits inside the UK’s customs territory. The Windsor Framework keeps it aligned with EU rules for goods that risk moving into the EU single market. Trader Support Service is how that commitment gets executed on the ground. TSS lets traders use a simplified, two-stage customs procedure for GB-NI movements: a Simplified Frontier Declaration at the border, then a Supplementary Declaration afterwards. It stays free to use, and it remains the main route most GB-NI traders rely on.
The move to a new TSS platform does not change any of this. It is an infrastructure change, not a change in customs law. TSS itself is not closing, and the GB-NI route stays fully in place. Only the digital front end is being replaced. The transition window is short: the new platform takes over fully from 20 October 2026, and the outgoing system disappears from 30 November 2026.
What’s Changing vs What Isn’t
Nothing about the underlying customs process changes. Supplementary Declarations remain the same legal instrument under the same simplified procedure. They are still due by the tenth calendar day of the month after the goods move, and the same commodity, origin and valuation detail is still required. HMRC’s guidance confirms that existing customs processes and declaration structures are being maintained, not redesigned. Traders already signed up for the outgoing TSS will be migrated automatically to the new service. No fresh registration is required.
The Hard Deadline: 30 November 2026
One obligation matters most in the run-up to 30 November 2026. A Supplementary Declaration is not complete until it shows as Closed on the TSS Portal — submitted, paid or calculated is not enough. HMRC’s bulletins set no formal penalty for missing the cut-off, but the exposure is still real: access to the outgoing platform disappears on 30 November, whatever is still open in it, while the underlying duty and declaration obligation does not disappear with it. HMRC is explicit that traders “remain responsible for completing and submitting your Supplementary Declarations and paying any duties due,” and that responsibility holds regardless of the state of the platform housing them.
What Traders Should Do Now
Traders and representatives should audit every open Supplementary Declaration now — anything sitting in Draft, Input Required, Pending Payment, Tax Calculation Verification or Fiscal Hold status. Declarations left open will not simply carry over to the new platform: HMRC has not published a carry-over mechanism, and the safer assumption is that anything unresolved must be dealt with directly through HMRC, outside the normal TSS workflow.
The TSS route itself is not going anywhere, and account continuity is already assured for anyone currently registered. Even so, treat 30 November as a hard operational deadline in practice. HMRC has not framed it as a statutory penalty date, but the alternative is an open customs liability with none of the current tools available to close it out.
Key Dates and Next Steps
From 20 October 2026, the new platform becomes the only route for pre-lodging movements. The outgoing TSS platform closes permanently on 30 November 2026.
If you have questions about how this affects your business or your outstanding declarations, please get in touch with us today. . This note is based on HMRC’s Trader Support Service guidance on GOV.UK and TSS Bulletin 227th Edition, published by the Northern Ireland Customs & Trade Academy: https://www.gov.uk/guidance/trader-support-service. It is a summary for general orientation, not customs or legal advice.