Certainly the worst! I returned my covid test kit using Royal Mail tracked 24 service. Since the 14th of September, it's been 7 days and my test provider hasn't received my tests yet. Their customer care call center? Just an automated music playing system basically. I have continually reached out to them on my delivery delay, just passive responses...no active solutions to the issues on ground. They even claimed to have delivered it to my test provider after which their delivery system revealed otherwise. I would rather send a package through a tortoise than through Royal Mail. Absolutely frustrating and disappointing service.