Milan’s Expo 2015 trade fair and several other large public projects, including one to build a highway in Libya, were caught in the crosshairs of fresh corruption claims, following an official being held on suspicions of bribery.

Ercole Incalza, who has served as a high-ranking public works official in seven governments and who recently started work as an outside consultant, was detained just days after Italy’s prime minister, Matteo Renzi, visited the site of the Expo fair and called for its 1 May opening to be “up to the standard of Italy’s image”.

Three others were arrested in the case and police across Italy were conducting raids on homes and offices as part of the investigation into 50 other individuals, the chief prosecutor said. Incalza is alleged to have directed public works to a businessman named Stefano Perotti, who was also arrested, in exchange for a cut of the proceeds.

Court documents in the case have also mentioned the son of a sitting minister, Maurizio Lupi, who heads the infrastructure and transport ministry. The documents allege that Perotti funneled work to Lupi’s son, Luca.

The allegation was strongly denied by Maurizio Lupi on Monday night, with the minister saying that his son was bright enough that he did not require special favours. “I have never asked anything from anyone for [Luca’s] work, and it seems to me that, given his curriculum, he doesn’t need it,” Lupi said

But a judge reviewing the matter said in court documents that the indirect hiring of Luca Lupi by Perotti could have been part of an “illicit quid pro quo”.

A wiretapped conversations between Lupi and Incanza from February of last year also purports to show how close the two were, with Lupi telling Incalza that he named the deputy infrastructure minister, Riccardo Nencini, to his post because he was “sponsored” by Incalza, according to the Ansa news agency.

Prosecutors did not specify how much they believed Incalza gained from the alleged scheme. But he is alleged to have had a corrupting influence on public contracts across Italy, including the Expo, the high-speed railway line in Milan, the rail line in Bologna, a highway in the town of Civitavecchia, and a major road in Libya.

According to a report by Anas, Italy’s national road agency, the Ras Ejdyer-Emsaad expressway crosses Libya from Tunisia to the Egyptian border, totalling 1,750 km.

Anas is listed as the project management consultant, in a contract worth €125.5m. The allegedly corrupt contract at the Expo involves the Italian pavilion’s Palazzo Italia, (Italian palace) that, according to the Expo website, is one of the focal points of Italy’s showcase pavilion.

“Palazzo Italia will continue to remain after the event, serving the city as a centre of technological innovation,” the Expo website says.

Raffaele Cantone, the head of Italy’s national anti-corruption authority, recently told the news agency Ansa that the Expo would soon open with a “few problems” but that its public contracts were clean, thanks to an agreement with the Organisation for Economic Co-operation and Development that had aimed to stem corruption in the exhibition.

The Milan Expo was hit by a series of alleged scandals last year.

