Leading the campaign is Fred Lambton, grandson of Lord Lambton, the former Tory cabinet minister who lived out his life in Tuscany after resigning from the Heath government over a call-girl scandal.
Others include models Rose Hanbury and Zita Lloyd; Joseph Getty, grandson of billionaire Sir Paul Getty; George Frost, son of Sir David Frost; Rollo Weeks, an actor; Arthur Jeffes, a polar explorer; Marissa Montgomery, founder of the Pussy Glamore lingerie range; and members of such society families as the Guinnesses and the Heskeths.
The Save Siena group claims there are already enough airports within driving distance of the city to serve its 55,000 population. The streets are crowded each summer for the Palio, a medieval horse race around the Piazza del Campo, a square which has been declared a world heritage site by Unesco.
Lambton, 22, heir to the Earldom of Durham and stepson of Jools Holland, the musician and television presenter, said: “I spent a lot of time out there when my grandfather was alive and I have seen what the airport would do.