Can full citizens of EU countries (such as British citizens) enter and leave other EU countries at will?

Specifically, yes! If you are a British citizen, you can go in and out of other countries! Abroad! For example, Australia! As long as you have a passport, you can go! No problem going anywhere! And as long as it's not a China passport, it's ok! Just like going to Japan! The special inspection of Asian passports for Asians is very strict, but if you get a British passport, the inspection will be very simple! And it is not strict! Specifically, the freedom of entry and exit of EU countries and Commonwealth countries is very simple! Only Asian countries have some problems!