Spent criminal conviction

[Joarry]

OH has an informal job offer with Nhs (middle management type, mostly desk based support type role). Something caught my eye and I’m now thinking he might have to do an enhanced background check. Is this the case for all Nhs?
he has a spent conviction from near 20 years ago. Not disclosed on the application as assumed it was spent but now thinking it will show up?
should he fess up now? Main issue is they are asking when he will hand in notice to current job but I’m feeling nervous that he shouldn’t do that until he has under gone checks?

Whether it will show up depends on the details. If he received a custodial sentence (which includes a suspended sentence) it will show up. If he did not receive a custodial sentence, it will only show up if it is what is referred to as a "specified offence". If you tell me what the conviction was (PM me if you don't want to post it publicly), I can advise as to whether it is a specified offence.