That link doesn't give a very good answer at all. Cautions are now covered by the Rehabilitation of Offenders Act 1974 and they are spent as soon as they are issued unless they are conditional cautions in which case they are spent once the conditions have been met.
However, CRB checks are only used for roles that are exempt from the Rehabilitation of Offenders Act so the rule of cautions/convictions becoming spent does not apply if you have to have a CRB check, although, cautions are "stepped down". This means that after a set period of time (10 years for category A cautions and 5 years for category B and C) the caution is no longer disclosed to agencies who undertake background checks.
There are two types of CRB check, Standard and Enhanced. A caution will appear on the Standard check until it is stepped down (5 years in your case) after which it will no longer be disclosed. For an Enhanced check, however, even after the caution has been stepped down it can still appear on the CRB check if the Police deem it relevant for the purpose of the check.