How do I demonstrate my interest in my subject on my personal statement?

You demonstrate interest in the subject you're applying for by giving examples of ways in which you've pursued a deeper knowledge of your subject outside of your A-level curriculum. This could be through books you've read, talks you've attended, or relevant work experience. For example, if applying for a French and Spanish degree, it is a good idea to mention any exchanges or trips to French or Spanish-speaking countries you've taken part in, and a couple of books you have read or films you have watched. However, if you are going to mention films or books, rather than just give a name you should state what particularly struck you or took your interest, or maybe even compare/contrast them. If the degree you are applying for requires an interview it is important to have a thorough knowledge of anything that you reference in your personal statement!