Exhaustive list of grounds for detention Article  5  (1)  (f) of the ECHR is most relevant in the context of migration, as it allows the detention of migrants in an irregular situation and asylum applicants in two situations: 1. to prevent unauthorised entry into the country; 2. to facilitate deportation or extradition of a person against whom such action is being taken (e.g. an order has been issued and there is a realistic prospect of removal). Regarding the latter, the ECtHR considers detention arbitrary when no meaningful action with a view to deportation is under way or being actively pursued in accordance with the requirement of due diligence.135 Like the other exceptions to the right to liberty and security, migration-related detention under Article 5 (1) (f) must be based on one of these two specific grounds, restrictively construed.136 For instance, the pre-deportation ground for detention (second limb of Article 5 (1) (f)) may in principle not be applied to asylum applicants, the ECtHR stated, since Articles 31 and 33 of the 1951 Geneva Convention as well as the national law precluded their expulsion before a final decision has been taken on their claim,137 unless there is “a true prospect” for executing the removal.138 In its 2010 report, FRA noted that for stateless persons the likelihood of successful removal is slim, as there is no country of nationality who is obliged to take the person back and the country of former habitual residence often denies admission to stateless persons who have left.139 With regard to detention to prevent unauthorised entry, according to the ECtHR, asylum applicants who have been granted formal authorisation to stay in a country (e.g. under EU law) cannot be held in detention under the second limb of Article 5 (1) (f) of the ECHR.140 Under the ECHR, in addition to the above typical grounds, detention of migrants in an irregular situation and asylum seekers might also be permissible for the purpose of securing the fulfilment of an obligation 135 ECtHR, Mikolenko v. Estonia, No. 10664/05, 8 October 2009; M. and Others v. Bulgaria, No. 41416/08, 26 July 2011, paras. 75–76. 136 See ECtHR, Yoh-Ekale Mwanje v. Belgium, No. 10486/10, 20 December 2011; A. and Others v. the United Kingdom [GC], No. 3455/05, 19 February 2009, para. 167. 137 ECtHR, R.U. v. Greece, No. 2237/08, 7 June 2011, para. 94. See also ECtHR, S.D. v. Greece, No. 53541/07, 11 June 2009, para. 62. 138 ECtHR, Nabil and Others v. Hungary, No. 62116/12, 22 September 2015, para. 38. 139 FRA (2010), Detention of third country nationals in return procedures, Luxembourg, Publications Office, pp. 25-26. 140 See, in this sense, ECtHR, Suso Musa v. Malta, No. 42337/12, 23 July 2013, para. 97. See, however, CJEU, K. v. Staatssecretaris van Veiligheid en Justitie, C-18/16, opinion of Advocate General Sharpston, 4 May 2017. prescribed by law in accordance with Article 5 (1) (b) of the ECHR. For example, a discussion emerged in 2015 on resorting to detention to enforce compulsory fingerprinting for Eurodac.141 In general, a balance must be struck between the right to liberty and the fulfilment of legal obligations under Article 5 (1) (b) of the ECHR.142 Factors to consider when balancing such issues include the nature of the obligation arising from the relevant legislation, including its underlying object and purpose; the person being detained and the particular circumstances leading to detention; and the length of the detention.143 In O.M. v. Hungary, the ECtHR reaffirmed its constant stance that, when detaining asylum applicants under Article 5 (1) (b), specific criteria must be met, namely there must be an unfulfilled obligation incumbent upon the applicant; the obligation has to be specific and concrete; and detention must be for the purpose of securing its fulfilment and not be punitive in character, and must cease the moment this obligation is fulfilled.144 4.3. Discrepancies between the EU and ECHR legal systems The permissible grounds for detention under EU law must correspond to or fall under either of the migration-related grounds or any other relevant detention grounds exhaustively set forth in Article 5 (1) of the ECHR. Establishing such link is not always easy, particularly for asylum-related detention. Deprivation of liberty to verify the applicant’s identity and nationality or to determine an asylum claim where this would not otherwise be possible because of, in particular, a risk of absconding can best be linked to the grounds in Article 5 (1) (b) of the ECHR.145 Detention of asylum applicants to protect national security or public order, although found by the CJEU to be lawful under Article 6 of the Charter,146 is difficult to subsume under any of the grounds set out in Article 5 (1) of the ECHR, except if detention is reasonably considered necessary under Article 5 (1) (c) to 141 See FRA (2015), Fundamental rights implications of the obligation to provide fingerprints for Eurodac, Luxembourg, Publications Office. 142 ECtHR, Göthlin v. Sweden, No. 8307/11, 16 October 2014, para. 58. 143 ECtHR, Petukhova v. Russia, No. 28796/07, 2 May 2013, paras. 58–59; and Vasileva v. Denmark, No. 52792/99, 25 September 2003, paras. 36, 38. 144 ECtHR, O.M. v. Hungary, No. 9912/15, 5 July 2016, paras. 42–43, which follows earlier case law (Göthlin v. Sweden, No. 8307/11, 16 October 2014, para. 57; Vasileva v. Denmark, No. 52792/99, 25 September 2003, para. 36). 145 See also e.g. De Bruycker, Ph. (ed.) (2015), Alternatives to Immigration and Asylum Detention in the EU. Time for Implementation, Final report of the MADE REAL Project, pp. 50-51. 146 CJEU, C601/15 PPU, J. N. v. Staatssecretaris voor Veiligheid en Justitie, 15 February 2016. 43