The Rehabilitation of Offenders Act 1974 applies to all types of sentence, whether it is a term of imprisonment, a fine, probation, absolute or conditional discharge, findings in a juvenile court that an offence has been committed, and convictions of certain offences in service disciplinary proceedings.
The length of the rehabilitation period depends on the sentence and runs from the date of the conviction. When the relevant rehabilitation period has expired, the conviction becomes 'spent' and usually will not need to be disclosed in the future, for example, when you are applying for a job (unless the job is specically excluded from the act by its nature ie working with children), completing an insurance proposal form, or applying for credit facilities or a tenancy of property.
Details are retained on the Police National Computer solely for the prevention and detection of crime. If your finger prints / dna are taken they remain on the computer indefinately for the above purposes.
The insurance one is more of a grey area.... the question being 'disclosure of a material fact' - this is the term most frequently used to enable insurers not to pay claims! If the question set of the insurer includes 'Have you been in an IVA or Bankrupt' you then have a duty to answer correctly and inform the insurer if this circumstance changes.
In my experience if it is on the application form it is deemed material to either the underwriting policies, risk or pricing of the insurance product and therefor could be used not to payout when you really need them to.