The EU’s anti-fraud office has opened an investigation into former European commissioner Neelie Kroes, who was accused of breaking ethics rules after leaked documents suggested she secretly helped Uber lobby the Dutch government. Kroes, a Dutch former vice-president of the European Commission, was a key figure in the Uber files, a cache of company documents leaked to the Guardian and shared with the International Consortium of Investigative Journalists. The documents appeared to show that Kroes, the EU’s top official on internet policy from 2010 to 2014, had offered to arrange a series of meetings for Uber with EU staff and Dutch politicians after she left office, despite restrictions during an 18-month cooling-off period. In a statement to the Guardian, the EU’s anti-fraud office, Olaf, said that “following a preliminary evaluation of the allegations” its director-general had decided to open an investigation. The agency declined to give details, citing the need to protect “the conduct of the investigation” and “safeguard the presumption of innocence”. It said: “The purpose of the Olaf investigation is to gather evidence, either inculpatory or exculpatory, in order to confirm or deny the allegations,” adding that it was empowered to interview relevant witnesses and people concerned. It also said: “The protection of the reputation of EU institutions lies in the heart of Olaf’s work and is instrumental for maintaining the trust of EU citizens in the broader EU project. Therefore any media reports about alleged facts that could undermine this trust are taken very seriously by Olaf.” The agency has not set a deadline to complete its investigation, but the average inquiry in 2021 took 25 months, meaning no conclusions may be drawn until mid-2024. The Guardian has contacted Kroes for comment about the Olaf investigation. She has previously denied any inappropriate behaviour. In July she said: “I did not have any formal nor informal role at Uber before that particular date of May 2016,” referring to the month when a requirement to seek EU approval to take jobs expired. When the cooling-off period ended in May 2016, Uber quickly announced her as the chair of its public policy advisory board. Following the revelations in July, the European Commission faced calls to set up an independent investigation into the allegations, while transparency activists accused the EU executive of complacency about the “revolving door” system where officials move into lucrative jobs in sectors they used to regulate. Social Democrat and Green MEPs asked the commission to consider financial sanctions on Kroes – effectively cuts to her pension – if it was found she had failed to act with integrity. The commission has consistently declined to discuss its correspondence with Kroes, having promised to write to the ex-commissioner to seek “clarification” about the allegations. “We will determine any possible further steps once Olaf has concluded its investigation. Before the facts are known the European Commission cannot draw any conclusions. In the meantime, we continue to cooperate with Olaf,” it said in a statement. The Guardian has contacted Uber for comment. The cab-hailing app previously noted that Kroes had left its advisory board in 2018 and said it had subsequently introduced new guidelines on lobbying, strengthening requirements and oversight. Paul Tang, a Dutch Social Democrat MEP who chairs the European parliament’s subcommittee on tax, welcomed the inquiry by the EU’s anti-fraud office: “Now I expect a serious investigation from Olaf and I expect the Commission to take it seriously.” He added that if Neelie Kroes had breached the ban on lobbying, “I think it should be very clear that the commission should send a strong signal that this should not pass and that she should face some sort of financial penalties.”