Hopping on the conversation about the Oxford comma as an editor trained in both UK and US styles.
To use or not to use it, that is the question. And the answer depends on the style you are following.
The
Chicago Manual of Style is used in most general publications (fiction and nonfiction) in the US. Its guideline is to use the Oxford comma but to also be aware that it might occasionally create ambiguity (e.g., "I was inspired to write by my mentor, J. R. R. Tolkien, and George Elliot"—using the Oxford comma here makes it sound like my mentor is J. R. R. Tolkien, which is
not true).
New Hart's Rules are a part of the
New Oxford Style Manual, which is used for UK style, and while they acknowledge the usefulness of the Oxford comma, they don't prescribe it in the same way the
Chicago Manual of Style does. In fact, a typical sign of a book being published in the UK is that it does
not use the Oxford comma. (Yes, the name "Oxford comma" is one of the biggest misnomers of the English language.)
Just to make things somewhat more complex, individual publishing houses may have their own preference regarding the Oxford comma regardless of where they are located or which style they are following. Independently published authors have the unique privilege of being the publisher and so able to set their "house style." So an indie author could follow the
Chicago Manual of Style in all respects but have a rather powerful dislike of the Oxford comma. They are able to instruct the editors they hire to not use it.
Personally, I like the Oxford comma, but I've learned not to set my proverbial flag on a hill when dealing with the English language unless something is definitely wrong. Which is a fancy way of saying it's not a hill I'm going to die on, either as a writer or an editor

.