The important thing to understand from the case I cited is that an employer owes a duty of care to his employee not to allow or indeed require the employee to undertake a system of work which leads to a foreseeable risk of injury. This is basic employers liability law since the 19C. So if your employer requires you to work x hours knowing that at the end of the work you're having to drive back home knackered, even listening to LBC, there is every likelyhood that the employer will be liable to you (and any other unfortunate injured when you nod off as well) for the resulting injuries.