The company rule is to fire the senior. Of course it is.
Depends on the size of the company and how long the manager has worked there. He should be disciplined, but often with long term members of staff that takes the form of a verbal followed by a written warning, and only after that can they be dismissed.
If it's a small company whose owner is of a similar mindset to the manager the only recourse is a work tribunal, (over here at least anyway.)
If nothing else it's a good reason to join a trade union, they'll have your back even if the management doesn't.
When I was a civil servant they employed a real creep who immediately started freaking out the women he worked with. He followed one lady around during her lunch hour; she went grocery shopping and on her return to the office he told her every item she had bought. He asked another woman what she would do if she was attacked/raped in the street where she got off the bus.
It was a creepy enough question in itself, but what made it doubly frightening was that he knew what bus she caught and where she got off. Both women immediately joined the trade union which is when I got involved. Despite having a sympathetic manager it was next to impossible getting rid of the creep straight away because this behaviour didn't surface until after he'd passed his probationary period. Fortunately, after a lot of work on both sides we were able to find out that he'd lied on his application form about previous civil service work, and that's why he was dismissed straight away.
Don't get me wrong, I'm all in favour of employment rights but they can be exploited by creeps.