Suppose that some firm has two managers of equal status and one manager perverts the course of justice by supplying false information to a solicitor. If the second manager becomes aware of this, but does nothing and takes no steps to correct the record, are they just as guilty as the first manager of perverting the course of justice, or is there a crime "party to conspiracy to pervert justice"?
Knowledge of a crime is not a crime
At common law, if you know a crime has or may have been committed, you have no obligation to report it. Statutes may impose such a duty such as mandatory reporting of suspected child abuse by specific professionals.
If you take active steps to conceal the crime then that can make you an accessory to the crime and that’s illegal.
In your hypothetical, the manager has no duty to report the matter to the solicitor, the other side or the police. They do owe a duty to their employer to act in their employer’s best interest and they may be disciplined if they don’t advise their employer of what they know but that’s not a criminal matter.