I don’t really have a huge problem with people *saying* North Lanes/Laines – but when you’re writing a book about a subject you need to display some level of authority. “North Laine” is the ‘traditional’ name, whether common or not. I’d have been happy if the book had mocked pedants for raising the issue as long as it had acknowledged it knew there was an issue.
Maybe caring about this makes me less Brighton than both you and Mr. Raven.
FWIW, people in the village where I grew up simply referred to the area as the ‘Funny Streets’.