As title says, how much chemistry would I need at the beginning of university level particle physics? If I decided to study it, would the fact that I don't have chemistry in my A levels could be a problem?
ETA: I mean, obviously you need to know what a photon, proton, neutron and an electron are. You also need to know what a nucleus is. But that's strictly speaking, nuclear physics, rather than chemistry. Chemistry is orders of magnitude too "big" for particle physics.
If you are interested in experimental physics, in particular if you plan to work on beam lines and detectors, you might want to learn some chemistry. Note that experimental equipment contains lots of stuff you are not familiar with from everyday life.
At the very least, you need to know which materials are toxic or otherwise dangerous, and treat them accordingly. The way some physicists handle beryllium windows, for example, is absolutely mind-blowing.