I’ve been watching a 2003 documentary from BBC’s “Timeshift” series called “Jet Set.” Jackie Stewart is in several scenes in it.
Stewart said he realized he was going to have to abandon living in the UK in 1968 because his accountant told him he stood to make £100,000 but, thanks to a “Labour” (= socialist) Prime Minister, he was going to have to pay £93,000 in income tax (Stewart won his first of three WDCs in 1969).
He said that F1 was so dangerous in those days that the odds of a driver surviving five seasons was only one in three. And since 1968 was his first season to earn big money, he didn’t have the luxury to wait for 10 seasons to pass to amass an estate that would let his family live comfortably if he were to be killed. So he upped stakes and moved to Switzerland.
The narrator also mentions that after his first WDC, Stewart was traveling so much from his home base in Switzerland that he spent a month out of each year in airplanes.
Stewart himself told that after the SST came, he flew back and forth to the US 35 times each year. The SST entered service in 1976, three years after Stewart retired. At that time 35 round trips between London and JFK would have cost about $100,000 (assuming his sponsors in the US weren’t footing the bill), which would have been a little rough on the household budget if he still had only been netting £7000 a year.
https://www.bbc.co.uk/iplayer/episode/m000l9v7/timeshift-series-3-18-jet-set
One other detail I forgot to mention. That BBC documentary I was talking about above focused on the rise of “jet setting” that came with the invention of the high-flying, pressurized commercial airliner. And one of the locations that came up often when discussing the lifestyles of the rich and famous was Monaco.
And Stewart mentioned that the biggest thrill of his life wasn’t winning an F1 World Championship, it was winning the Grand Prix of Monaco, because he was presented his trophy by Princess Grace, the former Grace Kelly. Which he said was apropos as it was called the Princess Grace of Monaco trophy.