Visa for taking up residence in France or Switzerland only for UK citizens:

If you are coming for less than 90 days per period of 180 days:
No visa or work permit required for France or Switzerland but a convention d’accueil will be required (equivalent to a work permit). The teamleader of the person coming to CERN should contact Jenny as early as possible to request preparation of the convention d'accueil. This document has to be signed by the French authorities and, at present, this process can take a couple of weeks.

If you are coming for more than 90 days
Living in Switzerland
No visa is required and related Swiss/French cards will be requested by the Users’ Office upon arrival.

Living in France
VISA D is required.
The team leader of the person coming to CERN should contact Jenny to request preparation of the documents which the person can then use to apply for a visa via their local French embassy. Related Swiss/French cards will be requested by the Users’ Office upon arrival.

You  can find all information on the CERN dedicated web page.

Please note that it is the Users responsibility to ensure that they have the correct documents and follow the required procedures for entering Switzerland/France.