A UK company sending people to work in Belgium now operates as a third-country employer. Three things follow. Your social security position runs through the UK-EU Trade and Cooperation Agreement rather than EU coordination rules, so you apply to HMRC for a certificate of coverage instead of a domestic A1. The Limosa declaration still applies in full, unchanged. And there is an immigration layer that did not exist before 2021, because UK nationals are no longer exercising free movement. The paperwork is heavier than it was, and the biggest risk is assuming the pre-Brexit routine still works.
Where the UK sits in the Belgian market
The UK remains the largest non-EU source of posted persons into Belgium, accounting for 32 percent of all posted persons sent from outside the EU, ahead of India at 26 percent. In 2023 the UK-to-Belgium route recorded 1,718 posted persons, concentrated outside the main construction and metalworks flows.
UK firms are also present in Belgian industrial work: they make up 4 percent of posting companies in the petrochemical industry, a sector where turnaround and maintenance assignments regularly cross the site-registration threshold.
Social security: HMRC, not an EU A1
Since 1 January 2021, social security coordination between the UK and the EU is governed by the Trade and Cooperation Agreement. In practice:
- UK employers apply to HMRC for a certificate of coverage confirming the employee remains in the UK National Insurance system. It performs the same operational function as the EU A1 and is what a Belgian inspector will expect to see.
- The EU has notified the UK that all EU states apply the detached worker exception, and Belgium has confirmed it will do so as a Category A country. That allows a temporarily seconded worker to remain under their home system for up to 24 months, provided the conditions are met.
- Apply before departure. A certificate obtained retrospectively, after an inspection has begun, carries far less weight, and without valid cover the working assumption becomes that Belgian social security applies, with contributions owed.
Limosa did not change
This is the part UK companies most often get wrong, because it feels as though leaving the EU should have moved things.
Limosa applies to foreign employers posting workers to Belgium. It is not an EU-internal mechanism, and being outside the EU does not exempt you. You still file at limosa.be before the first day of work, you still receive a LIMOSA-1 receipt that each worker must be able to produce to the Belgian client, and a single declaration still covers an anticipated duration of up to 24 months.
You must also give the Belgian Labour Inspectorate the identity and contact details of a liaison person who can be reached about the posting. Our complete Limosa guide sets out the filing in full, and the exemptions, with their exact day limits, are in Limosa exemptions.
The new layer: immigration
Before 2021 a UK national simply turned up. That is no longer the position. UK nationals are third-country nationals for Belgian immigration purposes, and depending on the length and nature of the assignment, work authorisation and residence formalities may apply on top of everything above.
The TCA does contain provisions for short-term business visitors, contractual service suppliers and independent professionals, but they are narrow, condition-heavy and not a substitute for checking the specific assignment. Two practical points:
- Check the immigration position at the same time as the social security position, not afterwards. They are separate assessments with separate lead times, and the immigration one is usually the longer of the two.
- Do not reason from a colleague’s previous trip. A three-day sales visit, a two-week commissioning job and a six-month site posting can each sit in a different category.
Belgian work authorisation is a regional competence, so the applicable rules and the issuing authority depend on whether the work is in Flanders, Wallonia or Brussels.
Check-in-at-Work applies exactly as before
Nothing about Brexit changed the site registration regime. Registration is mandatory for works on immovable property, excluding cleaning, and certain meat-sector activities, where the total value of the works reaches 500,000 euro excluding VAT. That threshold attaches to the works as a whole, not to your contract value, so a modest UK scope on a large industrial site is inside the obligation.
Three points that catch foreign contractors:
- It is daily. Registration happens before the person begins work, every working day, for every person.
- Responsibility is shared between the party sending the worker and the party doing the work, and the two must agree who registers and verify that it happened.
- You need a Belgian company number (CBE) and portal access to register at all. For a UK company with no Belgian presence this is a genuine lead-time item, and the obligation applies from day one.
From 1 April 2027, a Programme Law adopted on 30 May 2026 extends the obligation to registering both entry and exit, and adds the supply of ready-mixed concrete to scope.
The differences between the systems are set out in Limosa, Dimona or Check-in-at-Work.
What it costs to get wrong
Failing to file a Limosa declaration is a level 4 offence, the heaviest category in the Belgian Social Criminal Code, carrying the possibility of imprisonment alongside financial penalties.
Fines rose on 1 February 2026, when the Act of 19 December 2025 raised the multiplier applied to social criminal fines from 8 to 10. For some infringements the amount is multiplied by the number of workers involved, up to a maximum of 100.
Your Belgian client carries exposure too, through joint and several liability for your workers’ wages and through the withholding obligation: where a contractor has social or tax debts, the client must withhold 35 percent of each invoice excluding VAT for social security debts and 15 percent for tax debts, checked at checkinhoudingsplicht.be. That is why Belgian main contractors now screen foreign subcontractors before award, as explained in our guide for main contractors.
Practical sequence for a UK company
1. Confirm the immigration position for the specific assignment and the specific region. Start here, because it has the longest lead time. 2. Apply to HMRC for certificates of coverage for every posted worker, covering the full planned period. 3. Arrange a Belgian company number (CBE) and social security portal access if site registration will apply. 4. File the Limosa declaration before the first working day, and name your liaison person. 5. Have presence registration running from day one, not from the first invoice. 6. Treat every crew change as a compliance event: new person means new coverage certificate, new Limosa entry, new site registration, arranged before travel.
Keeping the paperwork and the site in agreement
With three separate regimes now in play, the failure mode is drift. A crew substitution nobody logged, a programme extended without revisiting certificates, a site where attendance lives on a clipboard.
The fix is to make the record a by-product of work rather than an administrative task done later. When arrival registers the worker automatically against the right project, the site record matches your declarations by default, and gaps surface while they can still be corrected. Suivo’s check-in-at-work runs on the same workforce management platform as time tracking, so compliance data also feeds hours and project costing rather than sitting in a separate system.
See how Cibor handles registration across Belgian sites.
A note on language
English is widely used in Belgian business and accepted by the authorities for many purposes, which remains a real advantage for UK companies. A site inspection, however, will be conducted in Dutch in Flanders and French in Wallonia, so a local liaison person is still worth having.
Post-Brexit rules sit alongside the general framework, which is set out in the full guide to Belgian obligations for foreign employers.
Book a free demo
If you are bringing UK crews onto Belgian sites and want presence registration that satisfies an inspector without slowing your work down, we will show you how it runs day to day. Book a free demo.
