If you are going to be working with vulnerable people, children or adults, you may be required to have an enhanced DBS check and this does require you to declare all convictions spent or unspent, however the older the conviction and the less relevant to your job role then the more likely it is that an employer/governing body will pass over it as being no longer applicable. Don't make the mistake of not declaring it on an enhanced check, a friend of mine forgot a conviction for cannabis when he was a teenager and several years later when he filled in for me while I was in hospital and he had to do an enhanced check to take on my role so didn't declare it. Social services picked up on it and he not only lost his job but also his career as it would now follow him forever with them, not that he had the conviction but that he didn't declare it, it's seen as a matter of trustworthiness.