R (Bourgass and another) v Secretary of State for Justice  UKSC 54.
Two prisoners - Bourgass and Hussain - had been held in solitary confinement for lengthy periods well in excess of the 72 hours which a Prison Governor may order and well in excess of the 14 days maximum that the Secretary of State for Justice may authorise.
The Supreme Court (Lord Neuberger, Lady Hale, Lords Sumption, Reed and Hodge) held unanimously that the decisions to keep the men in solitary confinement ("segregation") for substantial periods were not taken lawfully.
The decision rests on essentially English common law principles.
The relevant legislation included a requirement for the Secretary of State to authorise segregation in excess of 72 hours. It was not lawful for the Prison Governor to take that decision either himself or on behalf of the Secretary of State. Officials in the Ministry of Justice could issue the authorisation because, under the Carltona Principle, the decisions of departmental officials were to be regarded as the decisions of the Secretary of State. The common law also required procedural fairness in that prisoners had to be given a reasonable opportunity to make representations before a decision to authorise continued segregation was taken.
The court held that Article 6(1) of the European Convention on Human Rights did not apply in this context.
The single judgment (delivered by Lord Reed) extends to 37 pages and will require more detailed consideration. I will add at the end of this post any links to commentaries that may appear.
Prison Act 1952
Prison Rules 1999 Rule 45
Prison Service Orders with link to PSO 1700
The question of legal aid for prisoners was not in issue in the Bourgass case. The Court of Appeal has granted leave for judicial review to take place regarding legal aid for prisoners - see the decision at R (Howard League and Prisoners Advice Service) v Lord Chancellor  EWCA Civ 819 and the article by Owen Bowcott in The Guardian 28th July 2015. The permission stage for judicial review is, it seems, capable of producing considerable complexity in itself !
Additional Links on the Bourgass case:
Public Law for Everyone 29th July - Bourgass in the Supreme Court: Solitary confinement, the Carltona Doctrine and Procedural Fairness
The Justice Gap - Frances Crook - Clear risks and inadequate safeguards: the reality of solitary confinement in prison