A project like London's now-abandoned Garden Bridge would "never" happen in Paris, according to its deputy mayor, who has criticised the UK capital's free-market approach to development.

"We don't accept to give the management of public space to the private sector," said Jean-Louis Missika, who is responsible for architecture, urbanism and economic development in the French capital.

The Thomas Heatherwick-designed Garden Bridge, which was scrapped last month, would have been controversially owned and operated by a private trust.

"We have not the right to do that," in Paris, Missika said. "The Seine is inalienable. You have not the right to give it away."

Fewer tall buildings is "best solution" for Paris

Missika also questioned London's rampant skyscraper construction. In 2015, Herzog & de Meuron's 180-metre-high Tour Triangle became the first tower to gain planning permission in Paris for 40 years, but further approvals will be strictly controlled.

"London has I think 275 tower projects in the city," he said. "We have less than 10. And we think that we are right. We think the best solution with a city like Paris, which is a very dense city, is to have a very careful dispatching of high buildings to signal new centralities. But we don't want to transform Paris into Dubai or even New York.”

However Missika said he believed that Brexit "will bring London and Paris closer together," revealing that he has proposed to London mayor Sadiq Khan that the two capitals become "twin cities" so businesses can benefit from both locations.

Paris and London could work as "twin cities" after Brexit

"We have approached London to see if the two cities can work together as 'twin cities' so fintech [tech-driven financial services] in London can also have a base in Paris, inside the single market," he told Dezeen.

"This will help London to retain its financial dominance and help Paris stay ahead of Frankfurt and Amsterdam."

Recently Paris appeared to be trying to woo businesses from London with a host of new office towers. But Missika played this down, saying the two cities are "complimentary more than rivals," pointing out that many people already commute between them "like taking a suburban train".

"Paris and London form together the European megapolis," he added. "When compared to Shanghai or Mumbai, we need to have a transnational approach."

Missika took part in a panel discussion organised by Dezeen at the Maison & Objet fair in Paris on Friday, as part of the Dezeen X MINI Living initiative.

The panel discussed plans to revitalise Paris overseen by Missika and mayor Anne Hidalgo, who has declared she wants to "build the Paris of tomorrow".

Environmental policies are at the heart of their plans, Missika said. "The greening of the city is very important against climate change. When you green a city you can diminish the temperate from two to three to four degrees."

"We all know that diesel [emissions] and car traffic is one of the main subjects for quality of life and quality of the air," he added.

"We are working on new ways of sharing the streets between cars and all other forms of transportation including pedestrians, cyclists and all other forms of transportation."

Banning private self-driving vehicles

The city is planning to ban the use of private autonomous vehicles in the future to prevent congestion, he said.

"In say 2025 you will have mayors, not only in Paris, that we don't want to have privately owned vehicles in the city. They will be forbidden. The idea is not to get rid of all vehicles, but making sure that what we call 'zombie cars' [autonomous vehicles with nobody inside] are not driving in Paris."

Instead, Paris will work with robot-car providers to ensure only vehicles that provide a public service are allowed in the centre.

"Today a car is driving during five per cent of its life and parking during 95 per cent of its life," he said. "So if you keep the same system of people owning autonomous vehicles, it's totally crazy. We will have autonomous vehicles empty 95 per cent of the time. So you need a total revolution of the way vehicles are sold."

He added: "If we are not able to regulate the coming of autonomous vehicles early, it will be a mess. The city of Paris has the tools to manage this."

Missika said that Paris' hands-on approach to development and strict controls over land use meant it had an advantage over London, despite the two cities trying to achieve similar things.

"Mayor Khan has the same strategy as Mayor Hidalgo," he said. There is no difference in strategy. There is a difference in the tools they have to use. The free-market approach of London doesn’t give tools to manage this."

Reinventing Paris

Initiatives by Hidalgo and Missika to transform Paris include a relaxing of a previous skyscraper ban – put in place following a backlash against the Tour Montparnasse in the 1970s – to allow residential towers measuring up to 50 metres and office blocks up to 180 metres; and the launch in 2014 of Réinventer Paris, a competition seeking innovative urban solutions for 23 sites across the city. Winning projects by architects including David Chipperfield and Manuelle Gautrand were announced in February last year.

Earlier this year Hidalgo launched a second phase of the project, which seeks architectural ideas for some of Paris' subterranean spaces.

Another project, Reinventer la Seine, seeks "new possibilities of living on the water and along the banks of the Seine" between Paris and Le Havre, where the river flows into the English Channel.

As part of this project a new pedestrian bridge is proposed for Paris, but Missika said while private funds would contribute to its construction, the city would remain in control of the public areas.

Keeping public spaces public

Asked if Paris would ever adopt the same approach as London's Garden Bridge, Missika replied: "Never".

"I have a strategy for the little bridge across the Seine, that is totally different from the project of [former London mayor and Garden Bridge supporter Mr [Boris] Johnson, for the bridge on the Thames," he said. "We will ask people to build something with private money, but the public space on the bridge will be managed by the city. Of course we will accept a restaurant under it and a café on the side to finance everything, but the public space will stay public."

Paris adopts a different approach to London when it comes to urban development too, with the city insisting on retaining control of public space.

In London there is rising concern over "pseudo-public space" that is controlled by private landlords, but in Paris this approach is banned.

"In Reinventing Paris we have done exactly the contrary," Missika said. "We say to the private sector that you have to make some parts of your land accessible to the public."

"I think there is a very big temptation of segregation," he added. "When you see the condominiums in the US, they put private police in the entrance, a barrier, and you cannot enter. The question is what guarantee do you have that all the people, every day, every night, every day of the year, will have the right to access the space."

Guarantees over public access can be rescinded by private owners, Missika said, giving the example of a corporation whose office complex was crossed by a public footpath.

"After the terrorist attacks they decided to close it," Missika said. "I put a big pressure on them to reopen it. It has been a big fight. This kind of situation is always complex if you don't have management of public space."

Preventing segregation of rich and poor

"The question of how you manage the design of the city, of the streets, and who has the right to be in the streets, and how you share the rights of the different users of the public streets, is very decisive in future," he added.

"You also have the question of social mixing; a city where the poor and the rich can be in the same spaces because segregation is the worst problem for cities. You see it in Paris, you see in it London… The city that accepts segregation is a dying city."

Other panellists at the Dezeen X MINI Living discussion were Oke Hauser, architect and creative lead at MINI Living; Frédéric Chartier, architect and co-founder of Chartier Dalix; Edouard François, architect and founder of Maison Edouard François; and Jean-Christophe Masson, architect and co-founder of Hamonic + Masson & Associés.

You can watch a livestream of the discussion here.