General principles are part of the EU law with which the EU institutions and member states are bound to comply. General principles are applied by the CJEU and domestic courts when determining the lawfulness of legislative and administrative measures within the scope of EU law, and are also an aid to interpretation of EU law. Examples of general principles include non-retroactivity (i.e. that the retroactive effect of EU law is, in principle, prohibited) and the protection of legitimate expectations where, for example, an administrative decision is cancelled or revoked.

High

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/604516/Great_repeal_bill_white_paper_accessible.pdf

Annex A, A.8