From December 7, you can enter the UK only upon presentation of a PCR or express test 
the coronavirus strain has tightened entry rules for foreign travelers. Information about this appeared on the website of the Association of Tour Operators of Russia (ATOR).
So, from December 7, all tourists over 12 years old, regardless of vaccination status, will be able to enter the country only upon presentation of the result of a PCR test or an express test for an antigen for a period not exceeding 48 hours. It is noted that earlier persons under 18 years of age were exempted from the study, and the validity of the coronavirus tests was 72 hours before departure.
Also, all vacationers must fill out no earlier than 48 hours before departure of the Passenger Locator Form (PLF), after which they will receive a confirmation by e-mail in the form of a QR code, which must be presented at check-in for the flight.
Upon arrival in the UK, tourists are required to go into a ten-day quarantine and pre-book coronavirus tests, which will need to be passed by the end of the second and eighth days of self-isolation.
Earlier in December, the Montenegrin authorities were against the background the spread of the new strain of COVID-19 tightened the entry rules for vaccinated tourists. From December 3, foreign tourists can enter the country only upon presentation of one of the four established documents to choose from.