Yellow lines restrict the streets around the London store, but there are metered parking spaces nearby for just three pounds an hour.
In the worst case witnessed on Saturday, a 150,000-pound Bentley Continental GT spent four hours going around as its two women passengers shopped.
The car emits four times more toxic carbon dioxide than a Nissan Micra - and is the equivalent of driving a low emission car almost 170 miles.
One oil millionaire idled outside the shop for an hour - and he had also paid 20,000 pounds to fly the 120,000 pound Bentley from Dubai.
Decked out in expensive designer clothes and sunglasses, he drove half a mile from Battersea, south London, to take his wife and kids to the shops.
The Sun also saw a Mercedes S500 driving around for 60 minutes - belching out 3.5 kilogram of carbon dioxide.
Harrods, owned by Mohamed Fayed, declined to comment.