French partners at UK firms could be spared a 10% tax bill thanks to a landmark case being pursued by Linklaters' Paris partner Philippe Derouin.

At a hearing in the Paris Social Security Tribunal last week, Derouin brought a claim against French social security body Urssaf disputing a system that forces many French partners to pay approximately 10% on top of the tax they already pay under UK law.

As it stands, partners can choose to pay tax in the UK but they are currently forced to pay around 10% more in social security payments in France because Urssaf does not treat social security contributions as tax.

Derouin is arguing that the contributions do count as tax and should qualify under an existing tax agreement between France and the UK, which would exempt partners from paying tax in two jurisdictions.

Derouin is being represented by Flichy & Associes benefits and employee savings head Philippe Langlois and French advocate Emmanuel Piwnica.

The French Government has supported Derouin, arguing that Urssaf's stance undermines Anglo-French tax agreements. Derouin, himself a tax specialist, told Legal Week: "This is probably the first and last time I have been supported by the Government in a tax case. This situation affects all partners in UK professional service firms working in France."

An opinion is likely to be delivered before the summer, with a judgment in the autumn.