Starting from 2 April 2025, citizens of European countries will need to obtain an Electronic Travel Authorisation (ETA) if they wish to travel to the UK. This digital travel document can be applied for in advance.
Source: https://www.france24.com/en/europe/20250306-pre-travel-entry-scheme-opens-to-europeans-seeking-to-visit-uk-electronic-travel-authorisation-eta-europe
