MrsGee:
An important question: Where are you?
In England and Wales there is (officially) no such thing as a 'basic' CRB check. The lowest level of check is 'standard' (but many people confusingly refer to it as 'basic'). Such a check will (contrary to Eddie's post) ALWAYS show ALL convictions. It will also show all cautions unless they were deleted by the relevant police force prior to October 2009. (From that date onwards, cautions are no longer deleted from criminal records).
In England and Wales only employers and organisations within the 66 categories listed here are permitted to have access to CRB checks:
http://www.homeoffice...ons-guide?view=Binary
(However quite a lot of employers, including the Post Office, seem to illegally find ways around the rules).
Scotland and Northern Ireland also have 'standard' (as well as 'enhanced') checks which, as in England and Wales, will show all convictions and cautions. Again, the checks are only available to employers and organisations where the work will be within the 66 categories above.
However Scotland and Northern Ireland also have (proper) 'basic' checks. Those checks are available to all employers but they only show convictions and caution which aren't 'spent'.
So the answer to your question is largely dependent upon which part of the UK you're in.
Chris