Everyone knows that Google, Apple and Facebook are big, and that Uber and Netflix are fairly sizeable too.
But far fewer people are aware just how enormous Airbnb and its rivals have become not in the boulevards and piazzas of foreign cities, but right here, in the UK.
The scale of the growth is not only remarkable, but also largely untracked.
We are blind to the amount of short-term letting that goes on, said Ian Adams, cabinet member for Westminster Council, which estimates that as many as one in 15 housing units in the borough are being let as short-term rentals.
According to the last figures released by Airbnb, two million guests stayed at 64,000 London listings between 1 July 2016 and 1 July 2017, a growth of 49% on the previous year.
When you factor in rival short-term letting platforms such as Booking.com and TripAdvisor, then it’s clear we are in the midst of a short-term letting boom, which is causing intense pressure on housing stock and local communities.
It’s a real problem, said Mr Adams. We’ve got 8,000 properties that we estimate are being used for Airbnb-type activity – that’s 8,000 flats or houses that can’t be used for people that might be working or living in Westminster.
The issue goes back to 2015, when the Coalition government passed a law which relaxed the previously stringent rules on short-term lets.
To protect London’s existing housing supply, and reduce the impact on local communities, the government made it illegal to let residential properties for more than 90 nights a year.
But Westminster Council says the legislation is impossible to enforce.
Spending a day with Westminster’s Housing Enforcement Team, it was easy to see why.
We visited Park West, a handsome residential apartment block near Marble Arch. Nearly one in five of its 530 flats is being used as a short-term rental – which means it has more rooms than there are in the entire Ritz.
In order to confirm that a letting was breaking the 90-day limit, the council officers needed to speak to the host or their guests in person. On the day we visited, they knocked on 30 doors. Only one person answered – and he didn’t speak English.
After he closed the door, I asked the officer what that interaction meant.
We could count it as one day, because we’ve seen him, he said.
In other words, to catch someone breaking the 90-day limit, Westminster’s seven-person housing enforcement team – which is currently handling over 1,000 complaints – might have to go back to a flat 91 times.
In response to the 90-day cap, Airbnb introduced an automated hosting limit, which blocks out a host’s calendar for the year once they have reached 90 days of rentals for a single property.
However, Westminster Council say that it’s too easy to get around the cap by listing the same property on other rental websites.
That’s why, along with London Mayor Sadiq Khan and representatives from cities such as Edinburgh, Westminster Council is calling on the government to introduce a register of short-term rentals.
We need a registration scheme that enables local authorities to keep track on a nightly basis of which properties are being let and for how long, said Mr Adams.
The platforms agree, at least in principle. “We have zero tolerance for attempts to get around our measures and we have backed the mayor’s proposal for host registration, which would help ensure rules are applied fairly and equally to hosts on all platforms,” an Airbnb spokesperson told Sky News.
We support last month’s announcement by the Mayor of London to start working on a regulatory short term rental solution, said a spokesperson from Booking.com, calling for an enforceable legislative solution… underpinned by legislation.
However, the government is not currently pursuing such an option.
Landlords who let out accommodation on a short-term basis must do so responsibly and in accordance with the law, an spokesperson for the Ministry of Housing, Communities and Local Government told Sky News.
While industry has taken steps to drive up standards, we are encouraging the sector to work proactively with local authorities to stamp out bad practice.