DOC 4444
5.3.4 Vertical separation during climb or descent 5.3.4.1 An aircraft may be cleared to a level previously occupied by another aircraft after the latter has reported vacating it, except when: a) severe turbulence is known to exist; b) the higher aircraft is effecting a cruise climb; or c) the difference in aircraft performance is such that less than the applicable separation minimum may result; in which case such clearance shall be withheld until the aircraft vacating the level has reported at or passing another level separated by the required minimum. 5.3.4.1.1 When the aircraft concerned are entering or established in the same holding pattern, consideration shall be given to aircraft descending at markedly different rates and, if necessary, additional measures such as specifying a maximum descent rate for the higher aircraft and a minimum descent rate for the lower aircraft should be applied to ensure that the required separation is maintained.
MATS pt 1.
5B. Changing Levels 5B.1 Aircraft may be instructed to change level at a specified time, place or rate. 5B.2 An aircraft may be instructed to climb or descend to a level previously occupied by another aircraft provided that: (1) vertical separation already exists; (2) the vacating aircraft is proceeding to a level that will maintain vertical separation; and (3) either: (a) the controller observes that the vacating aircraft has left the level; or (b) the pilot has reported vacating the level. 5B.3 If severe turbulence is known to exist, instructions shall be delayed until the vacating aircraft is known to be at, or through, another level separated by the required minimum. 5B.4 Controllers shall exercise caution when instructing an aircraft to climb or descend to a previously occupied level. Consideration shall be given to the fact that aircraft may climb or descend at markedly different rates and, if necessary, additional measures such as specifying a maximum or minimum climb or descent rate for each aircraft shall be applied to ensure that the required separation is maintained. This is particularly relevant when the aircraft concerned are established in the same holding pattern.
So there is nothing stating that can not be done.
Only that "extra caution" should be given...
Can anyone confirm or deny that this descent CAN be made?
Cheers