The Upper Tribunal has granted an application for judicial review in a case concerning service of a curtailment letter, holding that:
(i) The effect of Article 8ZA of the Immigration (Leave to Enter and Remain) Order 2000 (SI No. 2000/1161), considered in tandem with the Home Office published policy, is that where the Home Office receives notification that an applicant has instructed a representative or has a new representative and the specified requirements are satisfied, the notification must be accepted and the Home Office internal records must be updated accordingly.
(ii) Conversely, where the notification is rejected for non-compliance with any of the specified requirements, both the applicant and the representative must be informed.
The “specified requirements” are that the new representative includes a signed letter of authority and is regulated by the Office of the Immigration Services Commissioner (OISC) or a solicitor. Apparently a barrister operating with a litigation authorisation certificate from the Bar Standards Board would not on the face of it be considered adequate by the Home Office. This is no doubt a matter of oversight on the part of the Home Office.
These procedural issues are dry but as the recent case of R (on the application of) Godwin Chaparadza v Secretary of State for the Home Department  EWHC 1209 (Admin) showed, where the Home Office gets it wrong it can have expensive consequences. In that earlier case, a substantial period of detention was found unlawful on the basis of flawed service of a decision notice. The Free Movement write-up of the Chaparadza case is: Zimbabwean national unlawfully detained after Home Office fails to serve immigration decision.
Source: R (on the application of Mustafa) v Secretary of State for the Home Department (2000 Order – notification of representation)  UKUT 407 (IAC)