What does NCTS Phase 6 actually change for UK transit declarations?

By Saurabh Goyal, Founder & CEO of Phlo Systems. Published 15 October 2026.

If your business moves goods under transit, through the New Computerised Transit System, then NCTS Phase 6 is not a background upgrade someone else deals with. It changes the message structure and workflow that every transit declaration runs through, and it requires the software filing on your behalf to hold current HMRC accreditation against the new specification. A system that was accredited for the previous phase does not automatically carry that accreditation forward.

The 30-second answer:

• What NCTS6 is: the latest phase of the New Computerised Transit System, the mechanism used to declare and track goods moving under transit procedures (including Common Transit) between the UK and other countries.
• What actually changed: the message formats and API workflow that transit declarations are built and submitted through. This is a structural change, not a styling one, and it sits underneath every transit movement, not just a subset of them.
• Why accreditation matters: HMRC requires software connecting to the transit service to be accredited against the current phase. Software built or approved against an earlier phase is not automatically valid against NCTS6.
• Who has to act: any trader, forwarder, or software provider filing transit declarations whose system has not specifically been accredited and updated for NCTS6.
• Where tradePhlo stands: tradePhlo Declarations already connects to HMRC's CTC Traders API and files live UK transit declarations under NCTS6. This is a live production capability, not a roadmap item.

What NCTS6 actually is

NCTS is the system HMRC and other Common Transit Convention countries use to control goods moving under transit procedures, the arrangement that lets goods cross borders with duties and import formalities suspended until they reach their final customs destination. Each phase of NCTS has corresponded to a revision of the underlying message specification and the API it runs on. NCTS Phase 6 is the current phase, and it is now live.

The distinction worth holding onto is between a transit movement and a transit declaration. The movement, goods travelling under transit cover, has not changed in concept. What has changed is the structured data format and workflow that the declaration opening, tracking, and closing that movement has to use. That is why NCTS6 reaches every transit declaration rather than a subset: it is not a new optional feature sitting alongside the old one, it is a revision to the pipe the data flows through.

Why software accreditation is the part that is easy to miss

A transit declaration is not typed into a web form the way some customs declarations are. It is submitted through software that connects to HMRC's transit service via an API, and HMRC requires that software to be accredited against the current message specification before it can be used to file live declarations. That accreditation is phase-specific. It is not a one-time badge that a system earns once and keeps indefinitely as HMRC's specification moves forward underneath it.

This is where the risk sits for anyone relying on a declarations system without a direct line of sight into its accreditation status. A system that filed valid NCTS declarations last year was accredited against a previous phase. Whether it is also accredited against NCTS6, and whether it has been updated to use the current API workflow rather than the one it originally shipped with, are separate questions that do not answer themselves just because declarations are still going out the door. The honest way to find out is to ask the software provider directly which phase their accreditation covers and when it was last renewed, rather than inferring it from the absence of an error message.

What the new API workflow means in practice

Alongside the message format, NCTS6 runs on an updated version of HMRC's Common Transit Convention Traders API, the interface through which accredited software actually exchanges data with HMRC's transit system: opening a transit movement, receiving the Movement Reference Number, recording arrival, and closing the movement out. A system built against an earlier version of that API has to be rebuilt against the new one, not patched around the edges, because the structure of the calls themselves has moved, not just the fields inside them.

For a trader or forwarder using third-party declarations software, the practical question is not "can we still submit a transit declaration today." It is whether the specific system doing the submitting is accredited and integrated against NCTS6 now, while the previous phase is still being wound down, rather than at the point a declaration is rejected or a movement cannot be closed.

Who is most exposed

1. Traders and forwarders relying on older or thinly maintained declarations software. If nobody has confirmed the system's accreditation status against NCTS6 specifically, the safest assumption is that it has not been confirmed, not that it is fine because nothing has visibly broken yet.
2. Businesses that treat transit as a smaller, secondary part of their customs operation. Transit volumes are often lower than CDS import and export volumes, which makes it easier for a transit-specific accreditation question to go unasked while attention stays on the higher-volume declarations.
3. Anyone using a system that was built or approved specifically for an earlier NCTS phase and has not been revisited since. Accreditation against a past phase is evidence the system worked once. It is not evidence that it works now.

What to check this week

1. Ask your declarations software provider, directly, whether they hold current HMRC accreditation for NCTS Phase 6, not just whether transit declarations are "still working." Those are different questions with different answers.
2. Confirm which API workflow the integration actually runs on. A provider can be accredited in principle while a specific customer's integration has not yet been migrated to the current API version.
3. Treat transit declarations with the same scrutiny as your import and export declarations, rather than as a smaller category that gets checked less often because the volumes are lower.

Frequently Asked Questions

What is NCTS Phase 6?

NCTS Phase 6 is the current phase of the New Computerised Transit System, the mechanism used to declare and track goods moving under transit procedures such as Common Transit. It introduces a revised message specification and API workflow that declarations software must be accredited against.

Does NCTS6 affect all transit declarations, or only some?

It affects the underlying message format and workflow that every transit declaration is built and submitted through, so it is not limited to a subset of movements. Any software filing transit declarations needs to be accredited and integrated against the current phase.

How do I know if my declarations software is accredited for NCTS6?

Ask the software provider directly which NCTS phase their current HMRC accreditation covers and when it was last confirmed. Accreditation against a previous phase does not carry forward automatically, and declarations continuing to go out without errors is not proof that the underlying accreditation and API integration are current.

Is this the same as the UK CDS changes for imports and exports?

No. CDS covers UK import and export declarations. NCTS is the separate system for transit movements. Both are live HMRC systems, and a software provider's accreditation needs to be current on each independently.

How Phlo Systems helps

tradePhlo Declarations connects directly to HMRC's CTC Traders API and files live UK transit declarations under NCTS6 today. It is a production capability already in use for transit movements alongside UK CDS import and export declarations, not a future roadmap item. See how tradePhlo handles UK customs declarations.

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Related reading:

• What is the UK Customs Declaration Service (CDS), and how do you submit an import declaration in 2026?
• HMRC's CDS report contracts expired 31 March 2026: are you still using TRE?
• Is your CDS post-clearance amendment process still valid after 16 June 2026?

Saurabh Goyal is the Founder & CEO of Phlo Systems. He spent 12 years building CTRM and ERP systems for global commodity trading houses before founding Phlo in 2016.