If you ignore the guidance they'll start issuing warnings. Those warnings are kept on file to help with potential employment tribunal cases.
In the UK: after two verbal warnings and one written warning you'll be fired. Or sooner, if your behavior meets the gross professional misconduct level. (You punch someone, for example.)
Talking to HR is like talking to the police - assume that nothing you say will be used to help you and that everything you say will be used against you. The difference between talking to HR and talking to the police is that you have more legal protections when talking to the police.
You can't get away with not talking to HR at all, but you can certainly be careful what you say.
Don't talk to Police: