Hi there UK MATS part1 Chapter 3 page 3
VMC Climb and Descent
To avoid excessive delays to traffic when radar is not available, controllers may
authorise an aircraft to climb or descend in VMC provided:
a) essential traffic information is given;
b) the pilot of the aircraft climbing or descending agrees to maintain his own
separation from other aircraft;
c) it is during the hours of daylight;
d) the aircraft is flying in visual meteorological conditions;
e) the manoeuvre is restricted to Class D, E, F and G airspace at or below FL 100; and
f) the aircraft is not in CAS-T.
Hope this helps