It is well established that Article 5(1)(f) permits the detention of a person with a view to deportation only in circumstance where “action is being taken with a view to deportation” (Chahal v United Kingdom (1996) 23 EHRR 413 at paragraph 112). In that case the European Court of Human Rights indicated that detention will cease to be permissible under Article 5(1)(f) if deportation proceedings are not prosecuted with due diligence and that it was necessary in such cases to determine whether the duration of the deportation proceedings was excessive (paragraph 113).

In some cases, where the intention remains to remove or deport a person on national security grounds, continued detention may not be consistent with Article 5(1)(f) as interpreted by the Court in the Chahal case. This may be the case, for example, if the person has established that removal to their own country might result in treatment contrary to Article 3 of the Convention. In such circumstances, irrespective of the gravity of the threat to national security posed by the person concerned, it is well established that Article 3 prevents removal or deportation to a place where there is a real risk that the person will suffer treatment contrary to that article. If no alternative destination is immediately available then removal or deportation may not, for the time being, be possible even though the ultimate intention remains to remove or deport the person once satisfactory arrangements can be made. In addition, it may not be possible to prosecute the person for a criminal offence given the strict rules on the admissibility of evidence in the criminal justice system of the United Kingdom and the high standard of proof required.