Hello everyone,

I’m looking for some advice because I’m a bit lost regarding the tax and administrative side of my upcoming work assignment in the UK.

I’ll try to summarize my situation:

I’m 30 years old and I work for a French company based in Nantes on a permanent French contract (CDI, cadre/forfait jours), with a gross annual salary of around €45k.

I currently live in France and I’m still fiscally attached to my parents’ address in Finistère, even though I don’t spend much time there anymore.

Upcoming situation:

In one month, I’ll be going on assignment to the UK for an English client.

It’s a detached worker contract through my French company, so I remain a French employee.

The mission is planned for 1 year, renewable once.

In practice, I’ll be living and working in the UK, but still paid from France.

Conditions:

• Housing + meal allowance: €1,335/month (to cover my expenses there)
• I’ll rent a flat in the UK entirely covered by this allowance
• Company car + fuel paid by the company
• Still on French payroll as a French employee

I have quite a few questions about what happens next:

• Will I remain a French tax resident, or can the UK consider me tax resident since I’ll be living there most of the time?
• Do I need to file taxes only in France, or in both France and the UK?
• How does it work in practice to avoid being taxed twice?
• For retirement/social contributions, do I continue contributing in France or also into the UK system?
• I’ve heard about the “183-day rule” - how does it actually apply in my case? If I go over that threshold, do I automatically become taxable in the UK?
• What would generally be the most advantageous setup in my situation, considering this is supposed to be temporary?

More generally:

• Is keeping an address in France enough to remain fiscally resident there?
• Are there any common pitfalls I should be aware of (banking, healthcare, paperwork, etc.)?

Since Brexit, I feel like a lot of things may have changed, so if anyone has already been in a similar situation or has useful information, I’d really appreciate it.

Thanks a lot!!