If it wasn't a grey area, why would the European Court of Human Rights be hearing it instead of a local employment tribunal? Lots of law is a grey area, with both sides putting their argument and a judge adjudicating.

On the other hand, an employer physically assaulting an employee (with or without warning) wouldn't need to be heard by the ECHR because there is so much law and precedent to say that employers can't do that.

This is a straw man argument, and it's really not worth debating.