First of all, once a conviction becomes spent, it will no longer be disclosed on a basic DBS check. The process is that when a check is done after that date, the DBS computer works out that it doesn't have to disclose it and so it isn't disclosed. If you do a check on yourself on the day after your conviction becomes spent, it should come back with nothing to disclose. There is no lapse period or anything else. The only thing that could interfere would be if you got another conviction while you were waiting for the first conviction to become spent, as neither would become spent until both reached their rehabilitation date.
When it comes to disclosure, the level of check depends on the content of the job, so you should have a reasonable idea of which check will be done. If you don't, then Unlock has some useful information here
. Any disclosure question can be interpreted as "what are we going to see on your check?", so you can answer accordingly. If the job has a basic DBS check, then once your conviction is spent you can answer no. If the job is eligible for a standard or enhanced DBS check, most employers are professional enough to phrase the question properly, but not all are. If you don't disclose something they then see on an eligible check, they would probably see it as dishonesty. If they did a standard or enhanced DBS check for a job that wasn't eligible, you can challenge the check before it is actually run, and the DBS will investigate. Any information they see that they don't have a right to see is technically a breach of data protection law, and if there are any repercussions for you, then the Information Commissioner's Office would be interested in hearing from you.
As Chris Stacey said: Although its not formally part of the sentence that is handed down in court, the criminal record that someone comes away with effectively becomes a second sentence, which can have a long-lasting, if not lifelong, impact.