They are, of course, an extension of the workplace, and as such the Company is liable for everything that happens at them. From fights, to sexual harassment, to the police being called, etc, etc
I once had to investigate a grievance from a Christmas party because an employee's wife (also an employee) gave another male employee a bj. I mean, who raises a grievance? I suppose the investigation did lead to the wife and other bloke being dismissed, but, **** me, a grievance
Christmas parties can **** off imo.