Charles Napier, 67, from Dorset, is accused of one count of inciting a child to commit an act of gross indecency, Scotland Yard said.
He is the half brother of MP John Whittingdale.
Police also charged a second man, Richard Alston, 69, from Suffolk, who is accused of five counts of indecent assault and three counts of gross indecency with a child.
The charges date back to the late 1970s and concern an alleged victim who was 11 years old at the time.
Both men are due to appear at Westminster Magistrates Court on July 29.