At one time cautions could be deleted from a person's criminal record after a certain amount of time (usually 5 years) had passed. It was up to individual police forces to decide whether to have cautions issued by them removed from people's records. (Some forces did it automatically, whereas others didn't).
So, if your caution was quite some time ago it MIGHT have been deleted from the records. However, in October 2009, a legal decision (by the Court of Appeal) meant that no further cautions would ever be deleted from the records. All existing cautions, and those subsequently added, now remain 'on the record' for the rest of a person's life. (Well, it's actually to the age of 100, but that's probably not relevant here!).
If your caution was not deleted prior to October 2009 (which could only have happened if it was issued before October 2004) it will still be on your record and it will appear on any CRB checks which are carried out on you.
Chris