Notes taken while on a job for an employer should reasonably be considered 'work product' and the property of the employer. They are not your diary.
Your work email account is not yours, its your employers, the same as your hard drive on your work computer, or the phone log on your work owned cell phone.
If you don't want them read by someone else, don't write them. If that makes you unable to do your job...........you should find alternate employment.
An interview is a different matter, to a point.
It clearly depends on whether the contents of any interview can be used at trial; if they can, then, you have a right not to self-incriminate, but you can also be (potentially) charged with obstructing a police investigation.
If there is an agreement that you are being interviewed only for disciplinary purposes, and that that can't be used at trial, then I think you can be obliged to cooperate the same way any employee who failed to discuss w/their boss how the workplace got trashed, could expect to lose their job.
The Charter does not protect your right to employment, only the right not to self-incriminate.