Brexit-Travel documents : until 29 March 2019, to enter the United Kingdom, the traveler must be in possession of a valid passport or national identity card. No visa is required.
As of March 30, 2019:
☛ if a withdrawal agreement is concluded and ratified between the EU and the United Kingdom, the conditions will be the same as at present until 31 December 2020: the traveler must be in possession of a valid passport or national identity card. No visa will be required.
☛ in the absence of an agreement, the UK Government has announced that national identity cards issued by the EU Member States to their nationals will remain valid until 31 December 2020 inclusive for travel to the United Kingdom.
Consequently, French and European nationals will be able to continue to travel with their passports or their only identity card until that date. From 1 January 2021, however, it is possible that travelers will need a passport. The UK government has announced its intention not to make European nationals subject to the visa requirement for short stays (less than 3 months).
Important: Travellers with identity and travel documents that have been reported lost or stolen are systematically removed by the British Border Force. It is imperative not to attempt to travel with a travel document reported lost or stolen (and therefore invalidated).