OSCOLA (the Oxford University Standard for the Citation of Legal Authorities) provides guidance on how to cite European Union legal sources, please see in particular section 2.6 of the OSCOLA guide (PDF, 448KB).
Please note that the OSCOLA guide was produced before the creation of the European Case Law Identifier. In order to learn how to deal with the European Case Law Identifier when citing cases, please see the guidance contained in the OSCOLA FAQs section.
Guidance for citing and referencing EU and retained EU legislation following Brexit can be found in the OSCOLA FAQs updates section.
Except in limited circumstances, retained direct EU legislation uses the same titles and citations as the EU original. This is the referencing approach taken in UK legislation creating and referring to retained EU law.
The update includes guidance on how to differentiate between EU and retained EU legislation when citing.