In an eight-month investigation, journalists posing as lobbyists contacted dozens of MEPs to check if some were prepared “to sell their services” — this weekend naming Spain’s Pablo Zalba Bidegain as the latest member ready to push amendments in the European Parliament against remuneration.

The European Parliament last week opened an inquiry after the British paper said the three MEPs had accepted offers of up to 100,000 euros ($140,000) per year in exchange for proposing amendments in the EU legislature.

The EU anti-fraud OLAF agency says the European Parliament has refused access to its premises, while prosecutors in the MEPs’ home countries are also becoming involved.

“There are concerns that multiple and conflicting jurisdictions in different countries might prevent a swift and thorough resolution,” Transparency International (TI) said.

“TI is calling for one authority to lead the investigation. As the majority of the alleged offences took place within Belgian jurisdiction, it believes the Belgian Public Federal Prosecutor is best placed to take up that role,” the anti-corruption group said.

In Brussels, a spokesman for Zalba’s conservative EPP stood by the MEP, saying “his case is different to the three others because when he was offered cash, he contacted his lawyers.”

The others named by the London weekly are Romanian Adrian Severin, Austria’s Ernst Strasser and Zoran Thaler of Slovenia.

Strasser and Thaler resigned, while Severin resigned from his party but denied committing any illegal act.

The EPP acknowledged that Zalba introduced an amendment, but said it was “because he agreed with the amendment,” adding: “He cannot be condemned because he met lobbyists.”

TI said the scandal underlined the need for a vast reform of the lobbying system in the European Union as well as the need for a single jurisdiction to prosecute.