TV presenter and socialite Tamara Ecclestone is said to have been "horrified" after receiving threats to reveal details about her personal life.
Glamorous Tamara, 27, contacted cops on Monday after getting a letter from an extortionist who warned her he was about to release lurid claims from a former close friend.
The heiress, who lives in a ?45million mansion in Kensington, West London, was interviewed by detectives who are now treating the incident as blackmail.
Officers are also planning to interview the former close friend referred to in the threat.
A pal of Tamara, whose 81-year-old dad is Britain's fourth richest person with a $4.2 billion fortune, said: "She was horrified to get the letter, which was quite intimidating.
"It was just an insulting slur meant to have been said by someone she knew years ago."
A spokeswoman for Tamara, who recently starred in her own reality TV show on C5, said: "The police are handling it."
The Metropolitan Police said: "We received a complaint regarding an inappropriate communication relating to the release of personal information. The allegation is being investigated as blackmail."
Stunning Tamara is the elder daughter of motor racing magnate Bernie from his marriage to second wife Slavica.
The couple ? now divorced ? also have younger daughter Petra, 22, who was married in a ?12million wedding extravaganza earlier this year.
Tamara lives with stockbroker Omar Khyami, 37. in a 55-room mansion in one of London's most exclusive streets.
She has complained of "many misconceptions" about her, saying: "People see me as pointless and spoilt. They judge me on the fact my dad has money."
