With apologies for the delay in posting ('cos I've only just seen the question):
Up until a few years ago, police forces had the discretion to erase cautions from the records after 5 years. (Some did; some didn't). The rules have now been changed and all cautions remain on record for life.
Cautions (other than those which were erased, as above) appear on both Standard and Enhanced CRB checks. (As Boxtops indicates, the relevant police force - and/or professional body, where appropriate - may add any further information, which they deem relevant, to an enhanced check, including unsubstantiated allegations against the subject).
The only checks which don't show cautions are those at Basic level (because they're deemed to be 'spent' immediately, and 'spent' matters aren't listed). However, while Scotland has Basic level checks available, they don't exist in England & Wales.
Chris
PS: When cautions were first introduced, one of the justifications given was that they would enable those who had committed only minor offences to avoid obtaining a criminal record. Now they've been made part of a criminal record anyway!