Half a dozen members of the European parliament earn more from second jobs than as EU lawmakers, according to analysis that raises questions about potential conflicts of interest.

The campaign group Transparency International EU found that 70% of the European parliament’s 705 members have side jobs. Just over a quarter (26%) of side jobs were paid, with six lawmakers earning more than their €120,900 (£103,000) annual gross MEP salary.

The highest-earning MEP declared €3m a year from a real estate business; another politician had a salary from his corporate law job that was almost as high as his MEP pay, while numerous parliamentarians benefited from company board memberships and the lecture circuit.

Of the top 20 MEP earners, nine were members of the mainstream centre-right European People’s party (EPP); a further six belonged to nationalist or far-right parties, or had been members of such groups in the recent past. The top 20 also covered two socialists; two liberals, including the former Brexit coordinator Guy Verhofstadt; and one independent, who was expelled from the liberal group.

That was Lithuanian MEP Viktor Uspaskich, whose €3m in earnings topped the list. He was removed from the liberal Renew group in 2021 over homophobic comments and now sits as an independent. A low-profile MEP, Uspaskich was reported by Lithuania’s public broadcaster last year to have given money to a website promoting conspiracy theories about the war in Ukraine and Covid vaccines.

In second place was French MEP Jérôme Rivière, who earned €220,248 on top of his MEP salary, mostly through his involvement in a financial services company. Rivière was elected to the European parliament as a member of Marine Le Pen’s National Rally, but later joined Éric Zemmour’s Reconquête party, before re-registering as an independent in 2023.

At no3 was László Trócsányi, a former Hungarian justice minister and member of the hard-right governing Fidesz party: he was estimated to earn €171,638 from a university rectorship and academic work.

Other MEPs who had high earnings – although the sums were less than their salaries as legislators – included Guy Verhofstadt, a former leader of the liberal group. He earned €131,988, mostly from company boards and appearances on the speaking circuit.

The French centre-right MEP Geoffrey Didier earned €115,200 a year working as a corporate lawyer at a firm where he is said to “advise and assist business leaders or financial organisations” in litigation, as well as other outside earnings. He said his work as a lawyer was “totally legally compatible” with his MEP mandate. “Regarding the potential lack of time, I have been unanimously recognised as an MEP very committed in my work,” he added, referring to leading roles legislating the EU’s Digital Services Act and Media Freedom Act. “I know many MEPs who do not have any legal or any other activity and who, however, do not work as much as I did.”

Monika Hohlmeier, a German centre-right MEP, declared €75,000 a year for sitting on the board of Munich-based BayWa group, an agriculture-construction-energy conglomerate that is on the EU lobbyist’s register. She said: “I believe that politicians should not only be active in the political ivory tower, but also have to engage outside parliament. It is important that they publish their activities and that is exactly what I have been doing for years.”

She stressed the independence of her decisions, adding: “The experiences that I have in the various organisations or at BayWa and the knowledge that I generate there enrich me in order to analyse different issues from different perspectives and make a carefully considered assessment of facts.”

The Flemish nationalist MEP Johan Van Overtveldt earned €30,000 a year sitting on the board of an Antwerp-based company Nbx BV which specialises in technology and payment systems. Van Overtveldt’s office said the MEP was a member of that company’s international board and “focuses on international expansion plans, outside the EU. Hence, no conflict of interests”.

The Guardian has contacted all named MEPs for comment.

None of the MEPs have broken any rules, but Transparency International EU said the range of second jobs, paid and unpaid, raised concerns about conflicts of interest and potential foreign interference, 18 months after the European parliament was rocked by the “Qatargate” cash for influence scandal.

“When we look at the contents of the declarations, we see that there are mistakes, we see that there are activities that could be conducive, potentially to a conflict of interest,” said Raphaël Kergueno, the lead author of the Transparency International EU study, which is based on MEPs’ public declarations of outside interests up to 24 April 2024.

He contrasted what he saw as parliament’s limited checks on MEPs’ declarations with more “proactive” checks in some EU member states, such as France. “That opens up the door to a whole host of problems: either conflicts of interest … [and] potentially an open door for entities that might try to funnel money from third country governments into the European parliament.”

After the Qatargate scandal, MEPs voted to tighten ethics and transparency standards. More than half of the top 20 biggest earners (13 MEPs) voted against an amendment that would have banned side jobs with organisations on the EU lobbyists’ register. The proposal ultimately failed after it was rejected by more than 90% of the centre-right EPP and Eurosceptic European Conservative and Reformists (ECR) group.

Transparency International is also asking whether MEPs busy with second jobs have time to focus on their parliamentary duties. The report shows that the average MEP with side interests has four activities, paid and unpaid, while 23 MEPs declared more than 10 side jobs.

“Some MPs have so many side activities which really raises the question of how they allocate their time,” Kergueno said.

“We want to make sure [not only] that there are no conflict of interest, but we also want to make sure that elected representatives are working full time for the citizens and not necessarily for their private interest.”

Transparency International is calling on the next European parliament, which begins its term in July after European elections, to ban all side jobs, paid and unpaid. In the absence of such a ban – which would have to be voted on by MEPs themselves – the campaign group would like to see more robust checks from the parliament on second jobs, that “puts in place the resources to also ensure that MEPs will not have a situation of conflict of interest”, Kergueno said.