From the latest CAP493 (MATS 1) . Section 1, Chapter 3
It surprised me too !
5C. VMC Climb and Descent
5C.1 Controllers may authorise an aircraft to climb or descend in VMC provided:
(1) the manoeuvre is restricted to Class D, E, F and G airspace at or below FL100;
(2) it is during the hours of daylight;
(3) the aircraft is flying in visual meteorological conditions;
(4) the pilot of the aircraft climbing or descending agrees to maintain his own separation
from other aircraft and the manoeuvre is agreed by the pilot of the other aircraft; and
(5) essential traffic information is given.
5C.2 The application of VMC climb and descent could result in TCAS RA being triggered.
Therefore, in Class D airspace when surveillance services are being provided, VMC climb
and descent shall only be used where authorised and in accordance with any conditions
specified in MATS Part 2.