R (Wey) v Pathfinder NHS Trust  EWHC Admin 672
When the Tribunal has decided on classification, the RMO cannot subsequently reclassify unless there is some change in circumstance of a significant kind which would enable a tribunal to take a different view if the matter were referred to them again. The remedy to the doctor and to the Trust would instead be to apply for judicial review of the decision of the Tribunal
A change made by the Mental Health Act 2007 is relevant to this case. See Mental disorder no longer split into separate classifications 3/11/08
The summary below has been supplied by Kris Gledhill, Editor of the Mental Health Law Reports. The full report can be purchased from Southside Online Publishing (if there is a "file not found" error, it means this particular report is not yet available online). More similar case summaries from the year 1999 are available here: MHLR 1999.
The RMO may not use s16 to overturn a tribunal decision under s72(5) by reclassifying the patient - R v Pathfinder NHS Trust ex p W  MHLR 142 Admin Ct
Points Arising: If a Tribunal reclassifies a patient, the treating psychiatrist cannot overturn this unless there has been a significant change in circumstances or further evidence that would enable the Tribunal to take a different view.
Facts and outcome: W was detained under s3 on the basis of mental illness, but reclassified as suffering from mental illness and psychopathic disorder by the Responsible Medical Officer, using his powers under s16 Mental Health Act 1983. He applied to a tribunal seeking release or reclassification to mental illness only. The tribunal did not discharge W, but reclassified him as suffering from mental illness only, using its powers under s72(5) of the Act. The RMO, noting that there was no current treatment needed for mental illness, and so if he was not suffering from psychopathic disorder his detention was not proper, reclassified him again to mental illness and psychopathic disorder, using his power under s16 of the Act. This was quashed in judicial review proceedings on the basis that the tribunal decision had to stand unless there was a significant change in circumstances or further evidence which would enable a tribunal to take a different view if the matter was referred to it again.
Possible Bailii link (not there when last checked, but it might have appeared since 0700 this morning!)