The principle of mutual confidence is a fundamental aspect of EU law. It implies that Member States should have trust in one another when implementing EU law. So, in Hedley Lomas (Case C-5/94, The Queen v Ministry of Agriculture, Fisheries and Food, ex parte: Hedley Lomas (Ireland) Ltd.) the United Kingdom could not prohibit the export of live sheep to Spain because it did not trust the Spanish authorities in applying EU rules on animal welfare. The only thing the UK was allowed to do was either to start an infringement procedure according to article 259 TFEU or complain with the Commission.
In the recent case N. S. (Case C-411/10 N. S. v Secretary of State for the Home Department et M. E. and Others), concerning transfers of a asylum seekers to Greece, the Court made a caveat to that principle.
At issue here is the raison d’être of the European Union and the creation of an area of freedom, security and justice and, in particular, the Common European Asylum System, based on mutual confidence and a presumption of compliance, by other Member States, with European Union law and, in particular, fundamental rights.
By contrast, if there are substantial grounds for believing that there are systemic flaws in the asylum procedure and reception conditions for asylum applicants in the Member State responsible, resulting in inhuman or degrading treatment, within the meaning of Article 4 of the Charter, of asylum seekers transferred to the territory of that Member State, the transfer would be incompatible with that provision.