Mill is so important to political philosophy that if you were to bring him up in your PS, you might be asked about him in your interview, and if you
seriously know your JS Mill (moreso than the standard joe who's just read 'On Liberty' in philosophy), they'd be impressed.*
*That is complete conjecture, but I've reasoned that it's gotta be roughly true 
I've got a friend who used to go to my school who's going to be applying for PPE (and he's seriously going to get a place; he's awesome), but me and another friend were just accompanying him as friends when he was meeting up with old teachers, and we visited my current philosophy teacher, and we ended up having a
huge and really deep conversation about Marx. My philosophy teacher wrote his PhD thesis on something to do with Marxism, and so knows it really well, and my other friend also has a profound knowledge of Marxism (although he's not a Marxist). It was just so insightful (read: strange) watching those two talk about really advanced concepts of Marxism (i.e. certain authors' interpretations of it, critiques, etc.) and me being able to chip in, having 'only' read DK, TGI & TCM. It was one of the best conversations I've had, but left me thinking that I might read a lot more on Marx, like dialectical materialism and famous critiques, and put it on my personal statement; though I can only imagine how cliche it must be for a 17/18 year old to say they have an interest in Marxism on their personal statement...

We then went to the pub and played 'Are you smarter than a 10 year old' on one of those quiz machines for money, and we were 1 question away from winning £5! The question was something like: "According to the Gospel's of Mark, how long did Jesus suffer on the cross for?". We thusly guessed it wrong, and spent the rest of the day crying.