I didnt understand that either. UK police "caution"? Do you mean "to get charged with an offence" or a warning? Very unclear and non-descript.
If you have committed an offence, it will be on your record. When they run checks, it is likely that they will find it. So, I would certainly declare it. Whether it will negatively impact your application is up to the officer and what he determines the weight of the offence to be. Meaning, if its a misdemeanor, it may not necessarily be the end...but if its felony larceny, they may very well be SOL.
Provide more detail and maybe people could respond better.