In the UK you have for a very long time been able to depart IFR without the need for any form of instrument rating.
That all changed with the JAA licence in July 1999. Schedule 8 and then 7 of the ANO stated that the privileges of the PPL(A) and CPL(A) were subject to the provisions of JAR-FCL 1.175 (one of the few JARs to be incorporated into UK Law.
JAR–FCL 1.175 Circumstances in which
an IR(A) is required
(a) The holder of a pilot licence (A) shall
not act in any capacity as a pilot of an aeroplane
under Instrument Flight Rules (IFR), except as a
pilot undergoing skill testing or dual training,
unless the holder has an instrument rating
(IR(A)) appropriate to the category of aircraft
issued in accordance with JAR–FCL.