According to a test carried out by The Reader's Digest, when 12 wallets were dropped in the Portugese city, only one was returned - and that, rather embarrassingly, was in fact found by a couple visiting from Holland. By contrast, in Helsinki, 11 made it back to their owners. London came equal ninth with Warsaw, with five of the 12 wallets being returned.
The researchers dropped wallets containing the equivalent of £30 in cash, along with a phone number, in 16 cities around the world. Despite the fact that this represented a great deal of money in India, Mumbai was the second most honest city in the sample, with nine people returning the wallet.
One of these, 27-year-old video editor Rahul Rai, said, "My conscience wouldn't let me do anything wrong. A wallet is a big thing with many important documents."
Only two of the 12 wallets were returned in Madrid, making it the second-least honest city in the sample. This figure backs up warnings from British consulates in Spain that pickpocketing and bag-snatching are on the rise - indeed, in Madrid, 362 emergency travel documents were issued last year, up nearly a quarter on the year before.
Police warn that holidaymakers should be careful of their possessions, carrying the minimum of valuables. Don't wear expensive jewellery, they say, and keep your passport, traveller's cheques and cash separate. And look out for pickpockets and thieves using distraction techniques, such as asking for help or spilling something on your clothes.
The global honesty test
1. Helsinki, Finland - 11 out of 12 wallets
2. Mumbai, India - 9 out of 12
=3. Budapest, Hungary - 8 out of 12
=3. New York City, USA - 8 out of 12
=5. Moscow, Russia - 7 out of 12
=5. Amsterdam, Netherlands - 7 out of 12
=7. Berlin, Germany - 6 out of 12
=7. Ljubljana, Slovenia - 6 out of 12
=9. London, UK - 5 out of 12
=9. Warsaw, Poland - 5 out of 12
=11. Bucharest, Romania - 4 out of 12
=11. Rio de Janeiro, Brazil - 4 out of 12
=11. Zurich, Switzerland - 4 out of 12
14. Prague, Czech Republic - 3 out of 12
15. Madrid, Spain - 2 out of 12
16. Lisbon, Portugal - 1 out of 12