United Kingdom is currently partially open to tourists and quarantine is required depending on where you’re coming from. The UK has dropped all plans for a covid vaccine passport. Source
Quarantine is required at government designated site or self-isolate at home. Travelers arriving from green-listed countries are not required to quarantine unless a mandatory COVID-19 test taken on or before the second day after arriving in the UK returns a positive result.
Face masks, covid passes and all restrictions have been dropped: https://www.bbc.com/news/uk-60047438
Updated Jan 20th 2022