Direct effect is the principle that allows individuals to invoke EU law in national courts. The discussion centred on the past, present, and future of direct effect, with Professor Gallo arguing that direct effect is an ‘unstable doctrine of classic and contemporary EU law’.
The Light Side of Direct Effect
Professor Gallo began the event by outlining the established aspects of direct effect. Direct effect has never been codified in the Treaties despite being part of the constitutional backbone of the EU. Instead, the case law of the Court of Justice of the European Union (CJEU) has played a key role in the development of direct effect. Professor Gallo noted that the principle had broadened considerably since its conception in the seminal case Van Gend en Loos.
Direct effect gives practical meaning to the rights afforded by EU law. Professor Gallo noted that a number of influential lines of EU case law could not have developed without direct effect, including Zambrano, which is one of the cornerstone cases on free movement rights and EU citizenship.
However, direct effect is under fire. It is a deeply contested doctrine, perhaps most explosively challenged by Brexit. That debate has evidently not concluded, with the UK Supreme Court hearing the Dillon case in October 2025 regarding, inter alia, the direct effect and primacy accorded to provisions of the UK-EU Withdrawal Agreement.
Professor Gallo highlighted the fact that direct effect has been a prominent target of Eurosceptic and populist groups. Several recent cases in EU law focusing on Article 19 of the Treaty on the European Union (TEU) and Article 47 of the Charter of Fundamental Rights have served as a trigger for intervention from the EU. Article 2 TEU could potentially soon join that group, further generating tensions between the EU and its Member States.
While the political controversy over direct effect rages on, it is undeniable that this principle has played a key role for ensuring that EU citizens are able to enjoy their rights. Professor Gallo explained that direct effect is a necessary precursor for the disapplication of conflicting national laws. Direct effect enables a review of national law, and without it, as he argued, the CJEU’s power to do so would be very superficial. Thus, direct effect is central to the ability to remedy a breach of EU law.
However, despite the decades-long development of direct effect and the essential role that it plays in EU law, the doctrine ironically still lacks clarity and precision. Professor Gallo then turned the discussion toward the shadows of direct effect.
The Dark Side of Direct Effect
Professor Gallo focused much of the discussion on the contentious aspects of direct effect, emphasising the outdated nature of the test for direct effect. The test for whether a provision of EU law is capable of direct effect requires evaluating if the provision is sufficiently clear, precise, and unconditional, as broadly derived from Van Gend en Loos. However, Professor Gallo claimed that this test lacks consistency and is not even taken seriously by the Court itself. Additionally, he argued that clarity and precision have been absorbed into the notion of unconditionality. If this is the case, then unconditionality becomes the core element of direct effect rather than having a multi-part test, which adds to the uncertainty surrounding direct effect.
Furthermore, the contemporary approach to Directives has dramatically shifted since the days of Van Gend en Loos. Despite the distinction between Regulations and Directives, as outlined in Article 288 TFEU, the boundary between two forms of legislation has slowly dissipated. This new reality requires clarity from the CJEU in order to best address the new issues that could arise with the expansion of the direct effect.
Seeing as horizontal direct effect can apply to some Directives nowadays, the coherence of EU law would be improved if the CJEU were to acknowledge that the approach to the direct effect of Directives has changed. Professor Gallo argued that this would strengthen the legal certainty and legitimate expectations that individuals have regarding their rights under EU law. His assessment of the importance of legal certainty, which is a general principle of EU law, is quite compelling: a transparent, open acknowledgement of the new state of direct effect would be beneficial, as it would make EU citizens more aware of their rights and obligations under EU law.
Professor Gallo characterised the jurisprudence from the CJEU as vague and unpredictable. The lack of a systematic approach to the development of the doctrine is concerning, particularly for a court often accused of being prone to judicial activism. As he noted, arguments from the CJEU are sometimes ‘whispered rather than written’, and he concluded that judges have a duty to guide those who invoke and apply the law. However, even if the CJEU has taken an inconsistent approach in its jurisprudence, Professor Gallo acknowledged that the Court must strike a delicate balance between countervailing interests. This issue is particularly amplified when dealing with horizontal direct effect, which allows private parties to hold each other accountable under EU law.
In response to the Eurosceptic critiques of direct effect, Professor Gallo argued that direct effect is not an ‘infant disease’ and emphasised the fact that it is not only on equal footing with primacy but also ensures that the principle of conferral is respected. Direct effect is what prevents the EU from ever writing itself a ‘blank cheque’. Professor Gallo’s argument shines a light on the true interaction between several core aspects of EU law.
Advocate General Biondi commented that Professor Gallo’s book was a timely read for judges and practitioners alike. He stressed the continued importance of direct effect and concluded that direct effect is still highly relevant, with national courts referring novel and complex questions to the CJEU.
The event closed with an audience Q&A and a reception.