Royal Mail rubbishness

It's my niece's 7th birthday today. I wasn't able to go and see her today. Being the organised type, I made sure I sent her birthday present on Saturday so it would arrive on time although just to make sure would definitely arrive today, I sent it by Special Delivery. Except despite Royal Mail's guarantee that it would arrive by 1pm, it hasn't shown up. I'm not impressed. What's the point of having a service to guarantee delivery if it doesn't actually guarantee delivery? Yes, sometimes in really bad weather conditions it can't be guaranteed, but this wasn't the case.