Former London mayor Boris Johnson may have moved on from merely embarrassing the U.K’s capital to making the entire country squirm as its Foreign Secretary, but he’s left one legacy that is currently driving people across London insane: the Boris Bus.

You see, this week London has been sweltering in temperatures that have pushed close to 32 degrees Celsius, or 90 degrees Fahrenheit. That may be positively wintry compared to parts of the U.S. right now, but it’s pretty hot for a breezy North Atlantic island where air conditioning is rare. In a country where people complain about any weather as instinctively as a knee jerks when hit with a mallet, this would always pose a challenge. But right now the hottest place in London isn’t some sun-scorched paving stone. Instead, it’s the non-air conditioned upper deck of the bus style commissioned—nay, actively promoted—by none other than Alexander Boris de Pfeffel Johnson. Welcome to Boris’s very own mobile oven.

I’ll explain how London landed these ambulant grill shacks in a moment. But first, look at all the anger Londoners are unleashing on the Boris bus’s shockingly high temperatures. Forgive the odd typo here, these people wrote their tweets while basically on fire.

These Londoners are burning up thanks to a design flaw so fundamental that Americans accustomed to mechanically cooled air for three generations or more may need to read it twice for it to sink in. So allow me to repeat.

The Boris Bus has no air conditioning. And you can’t open the windows.

To be fair, the bus does have an air-cooling system of sorts. It just doesn’t work. London started adapting the buses (which work on some but not all of London’s bus routes) to fix this ongoing problem last year, so at least now you can open the windows in some buses to get a sliver of breeze in. Many of them nonetheless remain unconverted. And when it gets as hot as it’s been this week, the buses become so sweltering you can imagine being arrested for animal cruelty if you brought a dog on the upper deck.

So how did London end up with such a dud? The New Routemaster bus—as the Boris Bus is known officially—first hit the streets of London in 2011. Its arrival was prompted by a populist appeal by Johnson to public nostalgia for a cancelled but much-loved older bus model. The original Routemaster bus, first introduced in 1954, had an open back, which meant you could hop on and off easily even when the bus was stuck at lights or in traffic. Feeling the wind in my hair as I poked my head out of a Routemaster (hanging on to a pole placed at the exit) was one of the more poetic experiences of my London childhood, but having a gaping hole at the back of the bus posed some obvious safety issues. And not only was the open back an invitation to accidents, it made the lower deck freezing cold in winter, while the high step up made them difficult to access for people who use wheelchairs or experience limited mobility.

The old Routemaster clearly had to go, but when they finally went in 2005, people still missed them. Boris Johnson’s answer was to partially resurrect it in a quirky, toy-like new design by Thomas Heatherwick, designer of another controversial, embattled Boris pet project, the Garden Bridge. Cute from the outside—the front and back both have a good-looking Ziggy Stardust streak of black-tinted glass—the Boris bus retained some features from the old Routemaster, such as a rear staircase, an onboard conductor and a back opening, but added a closing rear door.

The back end of a New Routemaster bus. (Chris Sampson/Flickr)

Unfortunately, it was a bit like the old bus had returned after a spell buried in Stephen King’s Pet Sematary. The upper floor’s low ceilings are claustrophobic, while the model's inefficient batteries frequently fail, making it revert to generating power from the engine and thus becoming even more polluting than the original model. In the era of contactless payments and Oyster Cards, the conductors the buses came with didn’t sell tickets and have gradually been sacked. This left drivers alone to monitor the bus at the front entrance, meaning that the back doors, the main point of the design, could no longer be opened. So, not just a screw-up, but an expensive one. The Boris bus costs almost twice as much to build as its better functioning predecessor.

Now that Johnson has moved on, the sweltering buses still on London’s streets may be his most visible legacy. They’re still haunting him too. This week it was suggested that his ineptitude might see him become “the New Routemaster of British Politics.”

For people who don’t live in London or Britain, there may well be a delicious dose of Schadenfreude in witnessing the ongoing shambles of both Boris and his buses. If you can squint your eyes so Johnson’s sickening racism goes out of focus, it must be fun to observe this testament to British politics’ yen for privileged incompetents. Locally, too, it’s true that a jaded electorate’s yearning for lols was partly a motor for Johnson’s initial rise.

You could say, in fact, that Boris’s appeal was not dissimilar to that of his buses. What could be more fun to have around than something that resembled an outsized replica of a 1950s children’s toy? Now that both the buses and Boris are everywhere, however, the degree of sheer incompetence involved in their creation has sunk in. We, the people who let them come into service, now feel queasy and can scarcely breathe. And with neither the buses nor Boris coming out of service in the foreseeable future, the journey may still have only just begun