HR may protect the senior person/work or with other witnesses to truncate story depending on pressure on them. Go only to the POSH committee. A posh committee must always have representation of someone not from the company, a woman and a legal person.
An enquiry will be setup. Remember it’s not about their intent but about impact on you.
Suggestion: It may sound difficult to do, but if someone makes inappropriate remark please try asking them kindly to refrain from doing so. If they continue post that, it’ll only make your case stronger.