Social Security (Persons Serving a Sentence of Imprisonment Detained in Hospital) Regulations 2010
In summary, certain benefits are available at all times to non-detained patients, civil patients, hospital order patients, and technical lifers. Determinate-sentence transferred prisoners (including s47 and s45A) are entitled only from their "release date". Indeterminate-sentence prisoners are entitled only from their actual release.
Extract from Explanatory Memorandum
2. Purpose of the instrument
These regulations are being introduced to correct drafting which has been held by the Court of Appeal in R (D and M) v SSWP  EWCA Civ 18 to be defective. ...
The Court of Appeal held that the wording of the existing provisions required an interpretation which meant that a person subject to an indeterminate sentence of imprisonment who was being detained in hospital for treatment for mental disorder would be eligible for DWP benefits when the tariff part of the sentence had been served. This is contrary to Government policy. These regulations provide a revised form of words in the relevant legislative provisions to ensure that such a person continues to be excluded from benefits when the tariff date has passed.
ThanksThanks to Gina Morgan (Finance Officer, Avon and Wiltshire MH Partnership NHS Trust) for emailing a link to the legislation.