R v Gordon and others [2007] EWCA Crim 165
The Criminal Justice Act 1967, s 67 continues to apply to sentences of imprisonment imposed in relation to offences committed before 4 April 2005; offences committed on or after 4 April 2005 are governed by the Criminal Justice Act 2003, s 240, so that the court has to order a
reduction for time spent in custody on remand.
Where s 240 applies, once the court has decided that credit should be given, it should say so, and is entitled to adjourn for appropriate information to be provided about the relevant number of days. If the calculation has not been made, or the court is uncertain about the time served, but considers that, in principle, the time spent in custody should be treated as time served, the court might properly direct that the period will be deducted after the appropriate calculation has been made, and adjourn that part of the process.
Thereafter, the calculation should be made promptly and the final decision should, save in exceptional circumstances, be concluded within 28 days. However, even if delayed beyond that period, it is permissible for the crown court to deal with what is no more than the final implementation of its order.