Arrest or criminal charge
A. There is no general obligation to tell your employer about an arrest or criminal charge unless there is something specifically in your contract of employment that requires you to do so.
If your employer does find out, the key issues are whether the charge has a bearing on your suitability to do your job, and whether your activities have brought, or are likely to bring, your employer into disrepute.
The question of suitability will depend on the nature of your job and the colleagues and customers you come into contact with.
Whether you can be accused of bringing them into disrepute will also depend on the nature of the offence, and your position within the company.
It would be unusual for this to be the case if the arrest was for something unconnected with your work. Examples from case law tend to involve high-profile individuals, behaviour of a sexual nature or theft.