Immigration Law Questions? Ask an Immigration Lawyer.
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Looking at your third question, you will need to answer it "Yes." because the word used is "violated" as opposed to "convicted". In the UK cautions are given for minor crimes; but you have to admit an offence and agree to be cautioned. You can be arrested and charged if you don’t agree. So, since you were not arrested, you can answer question #2 as "No." if this the only incident on your record. A caution is not a criminal conviction, but it could be used as evidence of bad character if you go to court for another crime. Further, the caution can show on standard and enhanced DBS criminal background checks. So, if you are dishonest about it, the US government may find out. As to your first question, you should let answer that YES or NO based on what you know to be true about yourself.
If you were arrested, then answer "yes" to Q2. If you have taken cocaine once or only a few times, then answer "No." to Q1. If your criminal history is otherwise clean AND you are honest, you should still have at least a 75% or better chance of obtaining the visa.