The frontrunner in Mexico’s presidential election has defended a proposed constitutional overhaul as business-friendly, arguing that popular votes for top judges will enhance democracy.

Investors “have nothing to worry about”, Claudia Sheinbaum, 61, told the Financial Times while being driven between campaign rallies in the capital in a modest Chevrolet family saloon, as well-wishers pressed against the windows to offer flowers ahead of elections next month.

Proposals by leftist President Andrés Manuel López Obrador, of whom Sheinbaum is a close ally, to open up the choice of top election officials and supreme court judges to a popular vote as part of the overhaul have sparked concerns about the rule of law in Mexico.

But Sheinbaum maintained: “What we want is more democracy in the country. And their investments will be guaranteed.”

Sheinbaum, who holds a commanding lead in the polls, has pledged to continue López Obrador’s “transformation” of Mexico with the aim of bringing greater social justice, improving public services and burying a “neoliberal” economic model that she says brought “atrocious poverty and inequality”.

The proposal to amend the constitution to let the public vote for supreme court justices and election commissioners has been one of López Obrador’s most contentious reforms, and his alliance lacked the two-thirds majority needed to pass it in the last congress. His Morena party hopes to try again after the June elections, which also include a vote for a new congress.

Only one country, socialist Bolivia, currently elects supreme court judges, according to the Federal Judicial Center.

The opposition believes the changes would destroy Mexico’s judicial independence, and investors have privately expressed concerns about risks to the rule of law. But Sheinbaum said institutional reforms were needed because the supreme court had “acted politically, not in terms of justice”.

Asked whether she believes in checks and balances, a major concern for civil rights groups and investors, she said: “I believe in freedom. I believe in democracy. And that the people should decide.”

Mexico will almost certainly elect its first female president on June 2. Most polls give Sheinbaum, who cut her teeth in student politics and later served as mayor of Mexico City, a double-digit lead over the main opposition candidate, entrepreneur-turned-politician Xóchitl Gálvez.

A skilful communicator with an instinctive popular touch, López Obrador — who is standing down after a single six-year term in line with Mexico’s constitution — has greatly expanded welfare programmes and more than doubled the minimum wage. Those measures reduced poverty and inequality, and won him enduring support among Mexico’s less fortunate.

At the same time, the president will hand his successor Mexico’s biggest fiscal deficit since the 1980s, having abandoned austerity in his final year in office. But Sheinbaum played down the gap, projected at 5.9 per cent of GDP this year, as a temporary blip.

“This is a one-year deficit because all the president’s strategic infrastructure projects are being paid for. Next year that will reduce significantly,” she said.

Sheinbaum believes there is scope to raise revenues further through better enforcement and technology. Pressed on whether her flagship promises of better education, health and infrastructure would require higher taxation, she replied “yes” before quickly adding: “But we’re not thinking about it in the first instance. We don’t want to propose a deep fiscal reform until we’ve really looked things over when we take office.”

Mexico’s economy has been transformed over 30 years by its free trade agreement with the US and Canada, and Sheinbaum is keen not to rock the boat, especially when US companies are considering moving production from China to countries such as Mexico.

“We need to take advantage of the opportunity the trade agreement with the United States and Canada gives us,” she said.

However, she wants the government to take a more active role in planning economic development to ensure that investment reaches poorer regions and that Mexico adds value to manufactured products rather than simply assembling components.

“You can’t just put any kind of company in any place, because different territories have different vocations, especially when it comes to natural resources like water,” she said. “We don’t think investment should just create jobs per se. We believe in well-paid jobs, and jobs with wellbeing.”

Beijing has made big inroads in Latin America this century, displacing the US as the biggest trading partner in most of South America, but Sheinbaum is clear where Mexico’s priorities lie. “We don’t have a free trade agreement with China and I don’t think we should have one,” she said.

With the US election later this year, the candidates are preparing for the possible return of former president Donald Trump, who has lambasted Mexico over trade, migration and fentanyl. Sheinbaum insisted the relationship would be “good”, even if Trump wins.

She spoke to the Financial Times after a rally in Coyoacán, a middle-class area in the capital’s south, where she gave an assured speech in blazing midday sun.

Recalling Mexico’s defeat of the invading French army in 1862, she painted her Morena party as the heirs of the patriots who defended their country. She denounced the opposition as the corrupt heirs of the traitors who invited a foreign emperor to govern them.

“What does Coyoacán want? Transformation or corruption? . . . Patriotism or subservience?” she asked the crowd, who chanted “Presidenta! Presidenta!”

López Obrador’s party has upended Mexican politics since his landslide presidential victory in 2018. It now controls two-thirds of state governorships and, with its allies, holds majorities in both houses of congress. This political dominance worries opponents, who recall that Mexico was ruled by a single party for 71 years until 2000.

Juanita Goebertus, Americas director at Human Rights Watch, said Morena’s proposals threatened judicial independence. “It would make it much easier for any political party that’s in government to control the nomination of judges,” she said.

Mexico is a key exporter of cocaine and fentanyl to the US and the country has become a battleground for rival cartels. Polls show security is a top voter concern but Sheinbaum believes she can bring down violent crime by deploying methods she used as mayor in the capital.

“We need to strengthen [the policy of] zero impunity in our country. It doesn’t matter who commits murder, murder has to be punished by the law.” She dismissed the opposition’s calls for head-on confrontation with the cartels, saying that in the past they gave security forces a “licence to kill” innocent civilians.

“Our vision is the construction of peace,” she said.

López Obrador has replaced the federal police with a new 130,000-strong National Guard run by the military, and has called in the armed forces to perform tasks traditionally handled by civilians, such as building train lines and running airports, ports and the customs service.

Sheinbaum says she is comfortable with the strategy because the military ultimately answers to the president.

“Maybe people don’t understand it from the outside, but it’s not militarisation,” she said. “The Mexican army comes from the Mexican revolution, it comes from a social revolution, it doesn’t come from the elites.”

A climate change expert with a doctorate in environmental engineering, Sheinbaum wants to accelerate Mexico’s transition to clean energy, using minority private investment with the state in the driving seat. “I dedicated my whole life, before my public life, to climate change. So obviously when we take office we’re going to push it,” she said.

Famously disciplined, Sheinbaum is keen to make clear that while she has been a loyal disciple of López Obrador during her ascent to power, she will govern in her own style.

Although Mexico has “historically been characterised by very strong machismo”, Sheinbaum believes her probable victory is proof that this is changing.

“I think machismo is being left behind . . . Otherwise, a female president would be unthinkable.”