A wheel bearing will audibly fail...
Not always. Excessive play in a bearing is also a reason for failure but you need to take the load off to detect it. There are many things that can cause a vehicle to fall short of the prescribed standards. Ever had a crack in the windscreen occur while driving? That's an instant "not up to WoF standard" that you could reasonably be expected to be aware of so I hope you immediately stopped driving and had the vehicle transported home.
But there is an "out" for things as pedantic as that. In order to be held accountable for operating a vehicle not being up to WoF standard, provided you don't just pay the infringement offence fee that an overzealous enforcement officer might issue, it needs to shown that you could reasonably be expected to know about the defect.