Sam,
The quick answer is No, there is no mandatory groundschool for either the CPL or the IR.
However, for the MEP course, there is a required 7 hours of groundschool and a written test. If the CPL includes the MEP (as is often the case), then it will have to include the MEP groundschool.
Having said all that, you should always expect a full brief and de-brief for every flight. In addition, the examiners will expect you to have a high level of knowledge of either VFR or IFR flight (depending on whether you're doing the CPL or the IR) and associated subjects, as well as a thorough knowledge of the aircraft you are flying. So, as well as full briefs and de-briefs, your school will ensure that you acquire the necessary level of knowledge along the way.
FFF
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