Renato Soru is a wealthy man. In 2000 he made it onto the Forbes list of world billionaires, and a year later the US magazine ran a profile on him and his Milan-based Internet company Tiscali, which was "snatching up competitors in the Netherlands, Germany, Switzerland, Belgium and the Czech Republic."

Fast-forward to 2014. Soru is still CEO of Tiscali, earning over €10,000 a month, according to his declaration of financial interests filed as a Socialist MEP.

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More than half of the 751 MEPs in the new European Parliament have outside activities that could influence their work (Photo: European Parliament)

He is not alone in listing outside activities that come on top of the €8,000 basic salary that MEPs receive monthly as well as up to €11,000 in travel and housing allowances.

According to a searchable database launched Monday (13 October) by Transparency International, over half of MEPs have listed outside activities in their declarations of financial interests.

Jointly they earn between €5.8 and €18.3 million a year on top of their MEP salaries, TI has found.

Their activities are not illegal, but they raise questions about potential conflicts of interests. Under beefed-up ethics rules starting with the new Parliament, MEPs had to fill out their declarations right from the start, in an electronic format.

The categories of revenue however only give an indicative image of how much MEPs earn outside the Parliament, with the highest category being €10,000 or more.

While 12 MEPs have listed this category, 45 others could also have combined revenues of over €10,000 as they list several activities in the lower brackets.

Along with Soru, there is a Romanian centre-right MEP, Daniel Buda, who earns over €10,000 a month as a notary and who also lists that he owns 179 sheep.

Liberal leader Guy Verhofstadt is also high up in the ranking, with revenues above €10,000 a month as a member of the board of directors of a Belgian investment company, Sofina.

He also earns between €1,000 and €5,000 a month for being a member of the board of an oil-and-gas company, Exmar, for chairing the board of the European Institute of Public Administration, respectively.

French centre-right MEP Rachida Dati, who was overheard on open microphones complaining to a friend how bored she is in the EP, also scoops another €10,000 or more from her activity as a lawyer.

An MEP who stands out in terms of number of outside activities is French Liberal Nathalie Griesbeck, who lists 68 different board memberships in the medical sector, all in the lowest category (€0-500/month), meaning that she could have extra revenues anywhere between €0 and €33,433 a month.

Transparency International also found MEPs in breach of the Parliament' code of conduct: seven declarations are completely blank, one MEP submitted his declaration three months past the deadline, and 46 declarations indicate an income in the previous 3 years of less than €1,000 a month.

Eight of those were also MEPs in the previous parliament, who should have declared their previous mandate.

"Listing vague terms such as 'director', 'consultant', 'freelancer', 'manager' or abbreviations such as 'RvC FMO' or 'ASDCAM', does not allow for meaningful monitoring of their potential conflicts of interest," Transparency International notes.

The watchdog says more detailed information in the declarations is needed "to allow a meaningful monitoring of potential conflicts of interest" and a revision of the financial thresholds which end with "€10,000 or more".