According to the EAT in Basildon Academies v Amadi the answer is no.
The details of the case
The Claimant in the case, Mr Amadi, was a Cover Supervisor at the Academies. He breached his contract by not getting his employer’s permission to work at Richmond upon Thames College, where he was accused of sexually assaulting a pupil and suspended. However, after the police investigated, no criminal action was taken. But, when the Academies heard about the incident, they dismissed Mr Amadi, claiming he should have reported the allegation made at Richmond upon Thames College, and also for not seeking permission to work elsewhere without permission.
Mr Amadi’s unfair dismissal claim was successful, and The Academies appealed, arguing that there was an implied duty for an employee to report allegations of misconduct, as well as an express duty in his contract to do so. However, when the EAT looked at Mr Amadi’s contract and the policies in place at the Acadamies, they didn’t find any express duty for the employee to report allegations against them, apart from those which were true, so the dismissal couldn’t have been fair.
What does all this mean?
Unless it is expressly stated in your employment contract, you will have a hard time getting a tribunal to agree with you.
In this case, there was also no legal requirement for the employee to disclose the information.
If there is a particular behaviour you want to consider ‘gross misconduct’ you must make it explicitly clear to your employees, or else you may find yourself taken to tribunal!