Why did they want to leave

The idea of leaving the EU started in the 1990s again. Many people felt like Britain was losing control over their own country and decisions that were supposed to be made in the UK were being made in Brussels. People wanted back control, but there were two other main reasons other than control.

1. immigration 

In 2004, the EU expanded and took in 10 new countries from Eastern Europe. The UK expected immigration from those countries to be around 13,000 people per year, but this estimate was far too low. In reality, hundreds of thousands arrived in the following years, with about 750,000 people migrating by the end of the decade. This unexpected increase made many people feel that the government had lost control over its borders. As a result, immigration became a major political issue and influenced how people viewed the EU. It also increased public concern about free movement within the EU and contributed to growing support for parties that wanted stricter immigration control.

2 Money

Britain was one of the EU's largest contributors and sent 14.7 billion pounds to the EU each year. So many people asked the question where is all this money going? This concern about money and whether the UK was getting enough value back became part of the debate. People believed that the money going to the EU could be going to things like the NHS or other UK public services.