# EU supremacy and direct effect (historical doctrines)

> **Key takeaway:** Direct effect: clear/precise/unconditional (Van Gend). Directives: vertical yes, horizontal no (Marshall/Faccini Dori); use indirect effect. Supremacy: Costa; UK vehicle was ECA 1972/Factortame. Post-exit: supremacy curtailed — see REUL/EUWA.

- **Jurisdiction:** England & Wales
- **Practice area:** Public Law
- **Last reviewed:** 2026-08-04
- **Interactive page:** https://kttclegal.info/library/notes/PublicLaw/eu-supremacy-and-direct-effect
- **Keywords:** direct effect, supremacy, Costa v ENEL, Van Gend en Loos, Marshall, Factortame, directive, horizontal direct effect

## What is this about?

While the UK was an EU Member State, EU law claimed supremacy over conflicting national law and could create rights enforceable in domestic courts through direct effect. Those doctrines remain essential to reading the case law archive and understanding how EU-derived rights entered English law; they no longer operate as an external supreme legal order in the UK after exit and the 2023 reforms.

## What is the core rule?

Direct effect (Van Gend en Loos): sufficiently clear, precise, and unconditional EU provisions can create individual rights enforceable nationally. Directives may have vertical direct effect against the state if unimplemented/incorrectly implemented (Marshall), but not horizontal direct effect against private parties (Faccini Dori), subject to indirect effect/interpretation duties (Marleasing) and incidental effects. Supremacy (Costa v ENEL): EU law takes precedence over conflicting national law, including later statutes, as a matter of the EU legal order — given domestic force in the UK historically via the European Communities Act 1972 (Factortame).

## What are the elements or test?

1. Is the provision treaty/regulation/directive?
2. Direct effect test: clear, precise, unconditional?
3. Vertical or horizontal situation for directives?
4. Can compatible interpretation (indirect effect) achieve the result?
5. For modern UK: has supremacy been removed for assimilated law (REUL 2023) and what does EUWA s.6 say about case law?

## Which authorities matter?

- **Van Gend en Loos (Case 26/62); Costa v ENEL (Case 6/64)** — Foundations of direct effect and supremacy in the EU legal order.
- **Marshall v Southampton AHA (Case 152/84); Faccini Dori (Case C-91/92)** — Vertical but not horizontal direct effect of directives.
- **R v Secretary of State for Transport, ex p Factortame Ltd (No 2) [1991] 1 AC 603** — UK House of Lords disapplying conflicting primary legislation under ECA 1972 while a Member State.
- **Retained EU Law (Revocation and Reform) Act 2023 (anti-supremacy reforms)** — Domestic reform ending EU supremacy effects for the assimilated-law era — check current text.

## How does this apply in practice?

Treat as historical/analytical doctrine for UK courts today unless a specific statutory bridge remains. Pair with retained EU law overview. Do not argue Costa supremacy as if still governing UK primary legislation.

## What are common pitfalls?

- Asserting horizontal direct effect of directives against private employers without more
- Ignoring Marleasing interpretative obligations in historical analyses
- Applying Factortame as current authority to disapply Acts post-exit

## When would a practitioner use this?

Reading classic EU/employment/equality authorities; explaining how EU rights historically overrode inconsistent UK rules.

## Quick reference

Direct effect: clear/precise/unconditional (Van Gend). Directives: vertical yes, horizontal no (Marshall/Faccini Dori); use indirect effect. Supremacy: Costa; UK vehicle was ECA 1972/Factortame. Post-exit: supremacy curtailed — see REUL/EUWA.

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*Reference material from [KTTC Legal](https://kttclegal.info/), not legal advice. Work product supports instructing solicitors and barristers under their supervision. England & Wales.*