He's Lord Peter, because he's the younger son of a duke. He has no substantive title of his own. I think there are a couple places where ignorant characters call him "Lord Wimsey" and he frosts them out for that faux pas; it's clear that it's the characters' error, not the author's.
His wife, by the way, is neither "Lady Wimsey" (who would be the wife of a "Lord Wimsey") nor "Lady Harriet" (who would be the daughter of a duke, as Peter's sister is Lady Mary, even after her marriage), but "Lady Peter", an odd locution which means she's the wife of a Lord Firstname. Real-life example: Winston Churchill's mother, Jennie, who was Lady Randolph Churchill.
Sayers made only one tiny error in terminology: when Peter's brother the Duke is on trial in Clouds of Witness, he is formally said to be in the peerage of the United Kingdom. That can't be; his title has to be older than the U.K. and he'd be in the peerage of England instead. On catching the error, Sayers tried to explain it away, but her explanation doesn't work. Otherwise, she's impeccable. Would that newer authors would learn from her.
no subject
His wife, by the way, is neither "Lady Wimsey" (who would be the wife of a "Lord Wimsey") nor "Lady Harriet" (who would be the daughter of a duke, as Peter's sister is Lady Mary, even after her marriage), but "Lady Peter", an odd locution which means she's the wife of a Lord Firstname. Real-life example: Winston Churchill's mother, Jennie, who was Lady Randolph Churchill.
Sayers made only one tiny error in terminology: when Peter's brother the Duke is on trial in Clouds of Witness, he is formally said to be in the peerage of the United Kingdom. That can't be; his title has to be older than the U.K. and he'd be in the peerage of England instead. On catching the error, Sayers tried to explain it away, but her explanation doesn't work. Otherwise, she's impeccable. Would that newer authors would learn from her.