An enhanced CRB can show anything which a senior police officer deems to be relevant to the check. For example, I know a teacher who found that her husband's conviction for downloading child porn (which she was aware of before they were wed) appeared on her CRB check. Similarly, a teacher has posted here to say that an allegation of 'grooming a child for sex' had appeared on his CRB check, even though he'd never been made aware of such an allegation.
The inquiry which followed the Soham murders strongly criticised the police for failing to mention unsubstantiated allegations of sexual misconduct by Ian Huntley on his CRB check. Since that time police forces tend to 'err on the side of caution', by including every bit of information that they have to hand.
An employer can not normally dismiss an employee for something which occurred outside of work. However where the actions of the employee (or other circumstances related to such actions) create a 'loss of trust' in the ability of the worker to continue in their job, the employer may lawfully dismiss the employee if no other reasonable option exists. (For example, an innocent person might be arrested as part of an investigation into the abduction of a child, leading to a great deal of 'gossip' within the local community. If that person worked in a toy shop, his employer might find that parents and children were then staying away from the shop, leading to a loss of profit. He could then lawfully dismiss the employee).
Chris