EU institutions must demonstrate that the disclosure of a document effectively harms the public interest if they want to deny publication, the European Court of Justice has ruled.

The EU's top court also said on Thursday (3 July) that papers related to international agreements should not automatically be exempt from publication.

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The ruling is the culmination of a five-year legal dispute between Dutch Liberal MEP Sophie In't Veld and EU governments over access to documents regarding the Swift agreement between the EU and US on transferring banking data.

In July 2009, In't Veld had demanded access to a legal opinion by the Council regarding the legal base of the Swift-agreement. The Council refused and appealed a ruling by the Luxembourg-based Court in 2012 which demanded publication, arguing that publishing the document would "negatively impact on the European Union's negotiating position" and that the analysis was "only intended for the members of the council."

In its new ruling, the Court said that "if the institution decides to refuse access to a document ... it must first explain how disclosure could specifically and actually damage the [public] interest."

The explanation "must be reasonably foreseeable and must not be purely hypothetical," it added.

"We are moving away from an EU of diplomats and decisions being made behind closed doors," In't Veld told reporters on Wednesday.

"There should not be an automatic exemption for legal service documents ... but they are routinely classified," she said, adding that the document at the heart of the row suggested that the legal basis of Swift was "unsound".

The Court's new ruling also states that documents on international relations or negotiations should not be automatically exempted from being publicly available.

The implications of the judgement on the EU's ongoing trade talks with the US, and other countries, would be "the $64,000 question", commented In't Veld.

MEPs are hoping to reopen talks with ministers on plans to rewrite the 10-year old regulation on public access to documents held by the EU institutions.

In the last legislative term, Parliament attempted to cut the number of exceptions from disclosing official papers and to reform the rules governing their classification.

But the commission, backed by a majority of governments, sought to tighten rules on documents "meriting special protection".

Their proposal would have blocked access to papers on competition cases looking at cartels, mergers and state-aid, court proceedings, infringement procedures, and internal EU legal advice.

In't Veld told EUobserver she would demand an end to the stalemate from Commission president nominee Jean-Claude Juncker, although she conceded that he is not regarded as a champion of greater transparency.

"Everybody should be able to request access to documents, but right now that is impossible. With such long procedures, the right of access to documents is in practice a dead letter."

"Having to litigate for five years is not transparency, even if we get the documents at the end," she said.