Is a caution for possession of a controlled substance a problem for me?
The fact that you have a caution on your record which appears to be a complete aberration from your steady, law abiding life need not debar you from a particular career, although as you already know, it will show up on any enhanced CRB. Jack Straw’s son was allowed to be a school governor despite a caution for possession of a controlled substance (albeit in a different class) and his open admissions to continuing to smoke spliffs while a student.