Perception isn't reality, but it matters. A new EY survey has ranked Paris above London as the most attractive site for foreign investment, for the first time since the accounting firm started doing reports on the subject.
Grading cities is obviously an art rather than a science - this is more about sentiment than hard capital flows - and the same survey still had London ahead as a tech hub.
The UK perma-bulls who believe Brexit will just be a historic blip should pay attention, nonetheless. One measure of a city's confidence and attractiveness is the number of cranes adorning its skyline as new office buildings are constructed. And while London is still throwing up plenty of its oddly shaped skyscrapers, there have been worrying signs. Meanwhile, Paris has embarked on an even more vigorous construction programme.
London's residential property bubble is deflating and office space under construction in the capital fell 9 per cent in the six months to September, according to Deloitte. It's still too soon to write London off, of course. Brexit hasn't happened yet, the UK capital remains a talent magnet and the weak pound makes investment cheaper for foreigners.
Deloitte notes that the volume of new starts for office construction did return to above-average levels in early 2018. There's still money sloshing around, interest rates are low and cool tech companies are replacing cautious banks as the city's landmark tenants. Google is building a "landscraper" in London - which will be as long as the Shard is high, apparently - and Apple is taking over a power station.
Yet, apart from the tech giants, there's a lingering concern about who is going to fill all of the new corporate temples. The amount of office supply set to hit London is high by historical standards, even after the drop in construction last year. Delivered volumes in 2017 were estimated at their highest level in 13 years, and there's at least 10 million square feet of new space due over the next few years.
Developers will be praying that the City of London's finance sector can reach accommodation with Europe after the exit from the EU.
Meanwhile, the proliferation of cranes in Paris has been impressive. In the six months to September, Deloitte data for the enlarged "Grand Paris" area - which at seven million people isn't too far below London - tracked a 5 per cent rise in office construction.
At 1.75 million square metres, the total volume of space being built was bigger than London's. The tenants taking up Paris space are certainly less glitzy than London's, for now. Government offices, law firms and a new "House of Europe" for EU bureaucrats won't bother the Brexiteers too much. But Uber and WeWork are leasing space in Paris too. Google and Facebook are investing in artificial intelligence hubs. And Brexit certainly won't hurt the Paris finance scene. Bank of America is looking to transfer more people than expected there in a 400-person move.
To argue that Paris might take London's place is a stretch still. But sentiment matters. Even if EY's is only one survey, it's a warning to Boris Johnson and company that there's too much complacency on one side of the Channel.