I'm not sure if there is anything analogous to the US Department Of Transportation in England, but we have to abide by pretty strict rules here in the USA regarding driving hours. A UPS driver cannot work over 14 hours on a shift, must have 10 hours between shifts, and cannot exceed 60 hours in a week without (IIRC) 38 consecutive hours before the next shift. That being said, we HIGHLY AVOID working drivers over 12 hours per shift, and try to take on a lot of extra help during the holiday peak season so that the work is distributed evenly.
From what I can tell from the article, these are probably inexperienced drivers who may be on their own in regards to organizing their delivery route, sorting packages on their vehicle, and learning their route. Because UPS has a centralized management system (as apposed to FedEx, for instance, which is contract based), we monitor every driver and can send other drivers to assist anyone who begins to struggle.
Its not unheard-of for UPS drivers to pee in bottles (and less often, poop in big plastic bags that are kept handy in the package cars). Its definitely not encouraged, but it happens, especially when you're on a rural route.
UPS drivers have it pretty good because of the collective bargaining that's available through the union. We're definitely going to have some rough days ahead of us for the next few weeks, but peak season is a big deal that we prepare for months in advance.