From what I have observed as I have been in England from time to time over the past fifty years, what he says is true. Yes, there was always the likes of White Chapel, and to see how England actually was while Edward was kind, but read the life of Charlie Chaplain or Keir Dulie, the socialist. But in general. Halevy had to right. Evangelicalism worked a revolution in English manners and mores, and Prince Albert was an examplar of it.
You’re right about Halevy being right, which means Dalrymple’s chronology is off. The changes began happening in the late 18th c.—Wilberforce’s campaign against slavery, the prison reform movement, founding of missionary societies, etc.
It’s interesting that an earlier poster said his wife told him that reading Jane Austen made him more polite but less sincere. Yeats’ brother told him the same thing, after he’d read Castiglione’s The Courtier. Which suggests the stiff upper lip values go back to the Renaissance, which means they come from Cicero and Stoicism.
The English managed to meld this aristocratic, non-Christian outlook w/ Evangelical/Methodist piety and reforming zeal. That’s quite an achievement.
As in his take on the London riots, Dalrymple manages to ignores the effect of mass immigration—tho’ the corruption of English manners and morals is probably as much a cause as well as a consequence of the invasion.