As of August 2, vaccinated Americans are allowed to enter the UK for non-essential purposes, including tourism.
But entering the UK isn’t as easy as flashing a vaccination card, as it is elsewhere in Europe. Travelers must take tests before departure and after arriving in the country.
Like many countries, the UK requires a negative COVID-19 test before arriving in the country. Both polymerase chain reaction — or PCR, for short — and antigen tests are acceptable.
Source: UK government