Europe's second-highest court has overturned a decision by the European Commission to allow the cultivation and sale of a genetically modified potato developed by German chemicals group BASF.
The General Court of the European Union said on Friday the Commission had failed to follow the bloc's rules when approving the Amflora potato, which is genetically modified to produce extra starch for use in the paper industry.
While Amflora is no longer grown in Europe - BASF withdrew the product in 2012, citing opposition to the technology - the ruling may raise new concerns about the EU's complex and much-criticised approval system for GMO crops.
It could also delay a decision on a separate Commission proposal to approve cultivation of a new type of modified maize developed jointly by DuPont and Dow Chemical.
"Because the Commission significantly failed to fulfil its procedural obligations, the General Court has annulled the connected decisions," the court said, referring to the Commission's approvals for both cultivation and sale of Amflora.
A Commission spokesman said the EU executive was analysing the ruling.
"The follow-up which the Commission could take would be to appeal on a point of law, but I can't respond to you now because lawyers are still looking at the judgment," Commission health spokesman Frederic Vincent told a regular news briefing.
Environmental campaigners welcomed the ruling, and said the Commission had no choice but to withdraw its cultivation proposal for the new type of GMO maize, known as 1507, or face a similar outcome.
"Today's legal judgment demolishes the Commission plans to rush through the approval of Pioneer-DuPont's GM maize 1507 for cultivation," Greenpeace's EU agriculture policy director, Marco Contiero, said in a statement.
Currently, only one GMO crop is grown commercially in Europe - an insect-resistant maize developed by Monsanto. It is sown on about 100,000 hectares (247,000 acres) of farmland, mainly in Spain.
That level is dwarfed by an estimated 170 million hectares of GMO crop cultivation globally, mainly in the Americas and parts of Asia.
While repeated EU scientific assessments have concluded that GMO crops are as safe for humans and the environment as their conventional counterparts, consumer opposition to the technology in Europe remains strong.
The surprise approval of Amflora was one of the first decisions taken by the EU's then-health commissioner, John Dalli, who took office in February 2010. Dalli was forced to resign from the Commission last year after being linked to a tobacco bribery scandal.
It was only the second time a genetically modified plant had been approved for cultivation in Europe, and prompted an angry response from environmental campaigners and consumer groups who strongly oppose the technology.
It also led to a legal challenge against the decision by Hungary, supported by other EU countries opposed to GMOs, including France, Austria and Poland.
The Commission first proposed the cultivation and sale of Amflora in 2007, following a positive scientific assessment by the European Food Safety Authority (EFSA).
Following the failure of EU government ministers and officials to approve or reject the proposal, the Commission exercised its power to grant approval unilaterally in 2010.
But in its judgment, the General Court said that following the publication of an updated scientific opinion by EFSA in 2009, the Commission should have submitted new proposals for approval by EU governments rather than simply adopting its 2007 version.
"The Commission infringed the procedural rules of the systems for authorising GMOs in the European Union," the court concluded.
BASF said the ruling vindicated its decision two years ago to move the BASF Plant Science headquarters to the United States and stop the development of genetically modified seeds for commercialisation in Europe.
"The ruling underscores that it was the right decision in January 2012 to focus our plant biotechnology activities on markets with future relevance."
BASF added the potato was deemed safe by the EFSA and that Friday's court ruling was about procedures and not about the scientific appraisal of the product.