A conviction for which you received a fine will be spent under the Rehabilition of Offenders Act after 5 years. However, when an enhanced CRB check is conducted the police will use some discetion in relation to spent convictions. For example, if the check is in connection with a job application working with the young or vulnerable then an enhanced CRB check will usually be requested and the police can choose to disclose convictions that may affect your suitability to do that job, depsite the fact the conviction is spent.
It is even possible that the police will disclose information about you that is held on the Police National Computer, even if it did not result in a conviction (for exampe if you were arrested but never cautioned or charged). This can sometimes cause problems for those innocent of any offence wrongly accused.