Okay kiddo, well, a long time ago in the United Kingdom, there were some people who didn't like Catholics very much. They thought that Catholics were bad and did not agree with the way they worshiped God. This is called anti-Catholicism.
One of the reasons for this was that a long time ago, there was a big disagreement between the Catholics and the Protestants. The Protestants believed that the Catholic Church was doing things wrong, and they wanted to make some changes. This caused a lot of fighting and some people got hurt in the process.
Over time, people started to calm down and some laws were put in place to help everyone get along better. However, there were still some people who held onto their negative beliefs about Catholics.
This caused problems for Catholics who wanted to live their lives and practice their religion peacefully. They were sometimes treated badly by others because of their beliefs, and this made things difficult for them.
Fortunately, things have gotten better over time and people are much more accepting of each other's beliefs and religions now. It's important to remember that everyone deserves to be treated with kindness and respect, no matter what they believe.