Edited from https://www.drake.org.uk/interviews/susanna-clarke-author-of-jonathan-strange-mr-norrell/
Question: You seem to specifically emphasize English magic throughout Jonathan Strange and Mr Norrell. It is rarely, as I recall, just magic that is returning — it is English magic. Is English magic very different from that of other places? Did other nations lose their magic as England did, and if so, is it coming back? Can you do English magic if you aren’t in England, or is it tied to the land?
Susanna Clarke's answer: This is an important question and I’m ashamed to say that I didn’t give it a lot of thought until I was nearing the end of writing Strange and Norrell.
Yes, you can do English magic if you aren’t in England. We know this because Strange does magic in Portugal, Spain, Italy and Belgium (and for an hour or so in America). Nevertheless English magic is tied to the land.
Let me see if I can explain this apparent contradiction. Human magic is borrowed from fairies — and fairies don’t think of magic as we do, as if it were something special. From their point of view it’s just part of normal life.
If a fairy wants something he asks his friends — the Wind, the Rain, the Hills and the Stars etc. — to help him get it. English magicians developed magic — made it less fundamental, less natural, but ultimately they were drawing on the goodwill of the English Wind, the English Rain, the English Hills and those Stars that you can see from the Sussex Wolds or Birmingham or Carlisle. So English magic was like a conversation between the magicians and England.
The reason English magic is particularly strong is because of John Uskglass - The Raven King, a child stolen from England and taken to Faerie, where he learnt fairy magic and gained a fairy kingdom, before returning to England to gain an English kingdom. He then taught his magic to other humans.
This wasn’t so much because he was a generous sort of person — he’s not usually. It was more because he had two sorts of subjects — fairies and humans — and he saw that he needed to get them to bond, to become one people. Getting them to do magic together was a clever way to do this.
On the other hand, how English is English magic? As we’ve seen it comes from fairies. And John Uskglass didn’t think of himself as English — not at first anyway. He claimed to be Norman, which (if it were true) meant that his grandfather would have come over from Normandy with William the Conqueror. And in the 19th century Jonathan Strange’s mother was Scottish.
At the end of JS&MN there’s a footnote about a Scottish magician and Scottish magic. And Jennifer-Oksana’s is an Introduction to The Books of Caribbean Magic (2nd Edition): a fun piece of fan fiction crossing JS&MN with Pirates of the Caribbean. Other countries do have their own magics — I can’t see why they wouldn’t.
On the whole I suspect English magic has the edge because of Uskglass.