If I'm writing a sentence such as "I saw the Police Officer walking in the park" am I supposed to capitalize the words Police Officer? As I haven't mentioned the name it's like that is his name, like as you'd say the Shop Keeper. I'm using his title as his name so does that mean I capitalize it?
However in a sentence like "Being a police officer is dangerous" I wouldn't as I'm not using it as a name?
You wouldn't capitalize police officer (or shopkeeper) as it's not a specific, official title. There are too many people who are police officers for the title to be specific, and figuring out how many people share that job title at a time is a good rule of thumb to use when figuring out if you should capitalize a job title or not.