Hi,
It all depends on what your sentence was.
You can use the Unlock Disclosure Calculator here to get an idea of whether and for how long you have to disclose:
https://www.disclosurecalculator.org.uk/You have to disclose unspent convictions to any prospective employer who asks. If you're not asked, you don't need to tell.
Once your conviction is spent, you don't have to disclose it and can tick "no" to all questions about convictions, unless the employer is exempt under the Rehabilitation of Offenders Act. This only applies if you're looking to work with children, vulnerable people, in certain security roles, the medical/legal profession, etc.