Update: In May 2019 a spokesman for Robert Szustkowski contacted the Guardian to complain about this article. The readers’ editor investigated and concluded that: there was a high public interest in journalistic scrutiny of the restaurant eavesdropping case in Poland, the effects of which were continuing; Robert Szustkowski was a newsworthy figure; coverage of him ought to be accurate; and appropriate opportunities to respond to coverage ought to be provided to him. Accordingly, this article has been clarified and augmented with information received after publication, and a footnote has been added containing an English translation of an excerpt from a Polish court decision, in Robert Szustkowski’s favour, about related Polish media coverage.

Concerns are growing in Poland about potential Russian involvement in a dramatic wiretapping scandal that rocked Polish politics in 2014, after reports emerged that the businessman convicted of organising the operation owed tens of millions of dollars to a Russian coal business.

Marek Falenta, a Polish businessman with interests in the coal industry, was convicted in 2016 of organising the operation, which involved recording 700 hours of conversations over the course of more than 80 meetings between senior politicians and officials at two Warsaw restaurants.

The people recorded included the interior minister, the finance minister, the foreign minister and the transport minister, all from Poland’s pro-European Civic Platform party, and the heads of the national bank, the supreme audit office, the government protection bureau and the central anti-corruption bureau. Two waiters were also convicted for their part in the affair.

The publication of the edited transcripts by Wprost, a Polish weekly, in June 2014 caused a sensation after it emerged that Radosław Sikorski, the then foreign minister, had described Polish defence ties with the US as “worthless”, and the head of the national bank had appeared to suggest to the interior minister that Jan-Vincent Rostowski, the then finance minister, be removed in exchange for the bank’s support for government policy.

The revelation of Falenta’s debts raises the prospect of Russian involvement in a scandal that observers say was a major factor in the collapse of public support for Civic Platform, ahead of elections in 2015 and the subsequent coming to power of Poland’s ruling Law and Justice party (PiS).

Joanna Kluzik-Rostkowska, a Civic Platform MP, said: “When the operation happened in 2014, we weren’t conscious of the extent to which Russia was prepared to interfere in other countries’ elections – in the United States, in Brexit, in Catalonia, in Germany.

“But now that we know what happened in those countries, we need a full explanation of what happened in Poland.”

There have long been questions over how Falenta and the waiters managed to carry out such a sophisticated and long-running wiretapping operation without any external help.

The majority of the recordings took place in a private dining room at Sowa i Przyjaciele, which was established in 2012.

In 2016, it emerged that the restaurant in Warsaw had been established by two then business associates of Robert Szustkowski, a Polish businessman and property developer who has lived in Russia. On 28 May 2019, in a legal claim filed on Szustkowski’s behalf in a Polish court, a lawyer wrote that Szustkowski “has no connection with the company Sowa i Przyjaciele or this restaurant”. At the time of the revelations of the eavesdropping and the initial political fallout in Poland, Szustkowski was serving as the chargé d’affaires at the Gambia’s embassy in Russia. After publication of this article, Szustkowski’s spokesman said the diplomatic appointment had been from July 2014 to August 2016 and had been made in appreciation of Szustkowski’s assistance, through his charity the Orimari foundation, in fighting an outbreak of ebola in the Gambia.

In the 28 May 2019 legal claim, Szustkowski’s lawyer wrote that it was not true that the Gambia had bought weapons from Russia during the period when Szustkowski had been its chargé d’affaires in Moscow. A reference to this effect in a book had resulted from a mistranslation of a press article, the lawyer wrote. The article had reported that the Gambia’s defence minister had been to military fairs in Russia, but not that the minister had bought any weapons, the legal claim said.

Ewa Domżała, a former business partner of Szustkowski, told the Guardian that Szustkowski had worked in businesses associated with Andrei Skoch, a Russian oligarch, for decades. After publication of this article, Szustkowsi’s spokesman informed the Guardian of an ongoing legal proceeding in Poland by Szustkowski against Domżała in which her credibility had been challenged.

Skoch, now a member of the Russian parliament, was included in April on a US treasury sanctions list “for longstanding ties to Russian organised criminal groups, including time spent leading one such enterprise”.

The Polish weekly Polityka alleged last week that in late 2013 or early 2014, Falenta travelled to Kemerovo in Russia to meet representatives of Kuzbasskaya Toplivnaya, a Russian coal company.

According to the report, the deal is understood to have left Falenta about $20m (£15m) in debt to the company. Intelligence sources cited by Polityka claim the meeting was facilitated by Szustkowski.

In a statement published by Wirtualna Polska, a Polish news website, Szustkowski denied cooperating or working with Falenta, although he did not deny having had contact with him. He also strongly denied connections with any foreign intelligence agencies or organised crime groups, and any connection with the wiretapping operation. After publication of this article, Szustkowski’s spokesman brought this statement directly to the Guardian’s attention. Asked expressly whether Szustkowski intended in the statement to deny ever having had contact with Falenta, the spokesman replied yes, Szustkowski had “fully and unquestionably denied having contacts with Mr Falenta”. In the 28 May 2019 legal claim, Susztkowski’s lawyer cited a Polish media interview with Falenta from 2018 in which Falenta had denied knowing Szustkowski.

Questions have been raised about the extent to which political pressure from figures associated with PiS, a major beneficiary of the operation, may have hampered official investigations into potential Russian involvement. Neither government nor law enforcement officials have commented on the revelations.

A former intelligence officer who was serving in a senior role at the time of the scandal said: “The connections to Russia were numerous and obvious at the time, but they were never properly investigated.

“The Polish intelligence services are, unfortunately, heavily politicised, and already in 2014, many senior officials knew which way the wind was blowing. It simply wasn’t – and still isn’t – in anyone’s interest to dig into whether the incoming administration was elected with Russian assistance.”

Sławomir Sierakowski of the left-leaning thinktank Krytyka Polityczna said: “The operation happened at the peak of Polish influence in the European Union, when Poland was a strong advocate for Ukraine after the Maidan protests.

“The Russians have been infiltrating Polish politics and trying to control the region for centuries – why would they stop now?”

• Note added 17 June 2019: On 12 October 2018, the court of justice in Warsaw found in favour of Robert Szustkowski in a case against some Polish media reporting of issues touched on in this article. The court said in part: “The defendant [a Polish media outlet] pointed out the plaintiff’s [Szustkowski’s] connections with the Russian mafia and the Russian special services. In the Court’s opinion, claims of this kind do harm to the plaintiff’s reputation because they are not supported by any evidence. The plaintiff is an entrepreneur, and any suggestions that he has anything to do with the mafia environment have a negative effect on his professional situation and commercial relations. Also, suggestions that he was connected with the so-called “wiretapping scandal” are groundless, because, as the case files show, the plaintiff has no criminal record, and those responsible for the “wiretapping scandal” have been brought to justice. In the Court’s opinion, any suggestions that the plaintiff has connections with the Russian mafia and the “tape scandal” are a form of abuse and should be reviled.” Legal proceedings brought in Poland by Robert Szustkowski against Ewa Domżała and, separately, against Polytika were continuing at the time this note was added.