If you deliberately turn up in a suit on the day of the investigation, thereby showing how seriously you take the accusations, then they can’t expect you to take a lorry out for the day dressed in your Sunday best. This would need you to go home again to change which would be the subject of travelling expenses since you have already reported for work. You will likely end up being sent home with a full day’s pay and a bonus night at home with the family. They make the rules let them live by them.