A caution is a formal warning that is given to a person who has admitted the offence. If the person refuses the caution, then they will normally be prosecuted through the normal channels for the offence. Although it is not technically classed as a conviction (as only the Courts can convict someone) it can be taken into consideration by the Courts if the person is convicted of a further offence.
Cautions are covered by the Rehabilitation of Offenders Act 1974 and become spent immediately (apart from conditional cautions which will become spent after 3 months). Unless applying for particular types of work (see below), a person who has spent cautions does not have to disclose them to prospective employers and employers cannot refuse to employ someone on the basis of spent cautions.
However, when applying for particular types of employment, for example, working with children or vulnerable adults, certain professions such as law, health care and pharmacy, senior management posts within certain sectors and employment where matters of national security are involved, the application form will state that it is exempt from the Rehabilitation of Offenders Act 1974. In these situations, you may need need to disclose your caution and it may be disclosed on your DBS criminal records check. See Q89 for further guidance on whether your caution will be disclosed.
Cautions will always remain on a person's record. There are only exceptional circumstances when a caution could be removed from a person's record and it is anticipated that such incidents will be rare. Examples of such possible circumstances are that it was found that the original arrest or sample was unlawful or where it was found beyond all doubt that no offence existed. Any requests that fit the above criteria should be directed to ACRO Criminal Records Office. Please see the link in the Related Information for further details.