If you are referring to spent convictions, they are spent under the Rehabilitation of Offenders act 1974, but this is specifically excluded by Firearms Acts. Otherwise the lifetime ban for anyone who has been sentenced to more than 3 years wouldn't/couldn't apply.
For purposes of the Firearms Acts there is no such thing as a spent conviction. You must include all convictions, including ALL motoring offences except fixed penalty and parking tickets, whether still recorded on your driving licence or otherwise - whether in Britain or abroad. Informal Cautions do not need to be mentioned, but