For citizens of the European Union (EU), it is relatively easy to enter the UK. They do not need to apply for a visa in advance, and they can live and work in the UK for as long as they want. However, following the UK's withdrawal from the EU (known as Brexit), EU citizens who arrive in the UK after January 1, 2021, will need to apply for settled or pre-settled status in order to continue living in the UK after June 30, 2021.
For citizens of non-EU countries, it is more difficult to enter the UK. They must apply for a visa in advance, and they must meet certain criteria in order to be granted a visa. The criteria include having a valid passport, proof of financial means, and a genuine reason for wanting to enter the UK.
The UK also has a points-based system for immigration. Under this system, people are awarded points for different factors, such as their skills, qualifications, and experience. People who have enough points are eligible to apply for a visa.
Overall, it is not easy for immigrants to get into the UK today. However, the process is easier for EU citizens than it is for non-EU citizens.