Well, I was always taught you don't put a comma before the penultimate thing in a list.
Then I learned that it was an OK thing to do and was called an 'Oxford comma'.
Yeah, or a serial comma. Common in the USA, not so much in the UK. That's a matter of style. And it can also be a matter of sense and clarity:
I'd like to thank my parents, God and the Queen - not good.
I'd like to thank my parents, God, and the Queen - makes more sense. But then it's not called an Oxford comma, it's just called a comma.
But do stay in pedants' corner! Who says mathematicians don't belong?!
DadDadDad, NHR is part of the Oxford Style Guide, a bible for writers and editors. If you're writing or editing and have a query about something, you can usually find the answer there. It's good to have an authority to show to clients to explain why you've made a certain decision.
And come on, the dash - or en rule - is the only punctuation we have a space before!
There's actually not a hard and fast rule for a lot of grammar issues in British English. Often, the answer is a matter of style, and depends on the reader, the context and the text you're working on.