The proposed sale of all or part of the state's controlling 50.6% share in ADP, which operates Paris Charles de Gaulle to the north of the capital and Orly to the south, is the most eye-catching of the slate of privatisations planned by Macron in a country that cherishes the protection of public services.

The sell-offs — utility Engie and lottery monopoly FDJ are also potentially on the block — are integral to Macron's drive to curb government involvement where he believes the private sector would better deliver investment and change.

But the ADP sale has united opponents. They accuse President Emmanuel Macron of "flogging the family silver" and warn of the perils of economic liberalism, citing Margaret Thatcher's unpopular reforms in 1980s Britain.

This month opponents launched a petition that could lead to a referendum on the ADP privatisation next year -- a risky proposition for a president shaken by a public rebellion over his pro-business policies and perceived as indifferent to the working class. The ballot would be held as re-election looms.

Three bankers advising clients over ADP said there was no clear idea how much would be sold or when. Macron's government has put the plans on ice for at least the nine-month period opponents have to try to garner 4.7 million backers — 10% of the electorate -- to secure their referendum.

"This sale is on hold for a while," said George Holst of BNP Paribas, which is advising ADP. The project "will depend on the government's will to impose its political line in a clear way."

A second Paris-based banker advising a potential buyer said they were not aware of any current contact between government and interested parties.

"We have told our client the process is delayed, perhaps even cancelled. We're all on standby," they said.

Macron had counted on the ADP sale to service France's debt and build up a fund to finance innovation. The state's shareholding is worth almost 8 billion euros at current market prices. Selling the entire stake would command a premium, while selling a smaller block might be more politically palatable.

The weekly newspaper Canard Enchaîné reported Macron had decided to scrap the sale but that no announcement would come until the referendum bid had run its course.

"The public does not understand the privatisation," Macron is quoted as telling a visitor to his office. "We must take our time. We mustn't act as if the referendum did not exist."

In Japan for a G20 gathering, Macron sidestepped a question on the report: "I am not going to say today what I intend to do."

"NEW-AGE THATCHERISM"

At the heart of the matter is a decades-old debate in France over what role the state should have in the economy. 

Boris Vallaud, a Socialist Party spokesman, described the privatisation plan as a "grotesque economic mistake". 

"ADP is not a business like others: it is a tool of national sovereignty, it is the hub of Air France, it is a strategic asset," he told Reuters days after launching the petition near Charles de Gaulle airport. 

With Vallaud that evening was an unusual grouping of legislators, including communists and moderate socialists who accuse Macron of placing corporate profit ahead of national interest, and conservatives loyal to the Gaullist tradition of a strong government overseeing strategic assets.

"This plan, like others from Macron, feels like new-age Thatcherism," Vallaud said.

Opponents of ADP's privatisation draw parallels with the sale of the motorway network in the mid-2000s, an unpopular move that still leaves many complaining of unfair toll hikes.

"With the highways, we saw that when you privatise it is no longer the common good that prevails, it is the pursuit of profit," said 60-year-old petition signatory Martine Louaire.

Conglomerate Vinci was the big winner of the autoroute privatisation and wants to build upon its 8% stake in ADP.

Supporters of the privatisation dismiss opponents's claims that France would be handing customs and border control over to private interests, and argue the private sector is better placed to transform Charles de Gaulle into a world-leading hub. 

On sale would effectively be the airports' shopping centres, hotels, car-parks and aircraft landing tariffs, said Roland Lescure, a lawmaker from Macron's party and rapporteur on the legislation that permits the government to sell its holding.

Lescure said the government would have the final say over landing tariffs if a dispute with the concession-holder erupted. The plan, he said, had become mired in mistruths and wrongly politicised.

"It became a political fireball that everybody wanted to play with, especially in the context of the ‘Yellow Vest’ protests."

MARKET CONDITIONS

ADP would be a big prize for Vinci. 105 million passengers use Paris' two main airports annually. ADP booked 4.5 billion euros of revenue in 2018.

But as opposition has mounted to the company's privatisation, Vinci chief executive Xavier Huillard has downplayed the importance of ADP to the company's strategy.

Vinci had opportunities to grow its airport concession business with or without ADP, Huillard said in February, just as he finalised a 2.9 billion pound swoop for control of Britain's London Gatwick.

ADP chief executive Augustin de Romanet rejected the suggestion Macron's government is having second thoughts.

"The impression I have is that this (referendum bid) is not creating any trouble inside the finance ministry or the prime minister's office," Romanet told reporters this week. 

Finance Minister Bruno Le Maire has said he still believes in the privatisation.

Although the delay pushes delicate political decisions closer to an expected Macron re-election bid in 2022, Lescure said the president would not stop reforming France.

More of a concern, he said, will be the market.

"I hope the delay is not going to change market conditions."

(Reporting by Richard Lough, Inti Landauro and Elizabeth Pineau in Paris; additional reporting by Cyril Altmeyer and Chris Gallagher in Tokyo; Editing by Luke Baker and)

By Richard Lough and Inti Landauro