Always check your employer's handbook, if one exists, and follow any grievance procedure it sets out. Additionally, you should ensure that you follow the Acas Code of Practice to avoid being penalised in case of an Employment Tribunal.
It's a good idea tackle any workplace issues which come to light at the earliest opportunity, even before an employee has raised a grievance. If you can nip any problems in the bud, this will save a lot of time and money in the long run.
If you have received a formal written grievance, you should act immediately. The first thing to do is arrange a meeting, ideally within five working days. Remember that the employee is entitled to bring a companion to this meeting; this can be a colleague or trade union rep.
After the meeting, decide what action, if any, will be taken to tackle the grievance and communicate this decision to the employee without unreasonable delay. Set out the details in writing, along with the employee's right of appeal. For more information read Appeals.