I'm sorry, while I noticed the part you were trying to pay attention to, it was easily overshadowed to me by the fact that Bill Nighy voices the father, one of my favorite character actors of all time, especially in his roles in The Boat That Rocked (Otherwise known as Pirate Radio to fellow Americans), and Wild Target, the latter which definitely does a great job showing his acting range. Both movies that I would recommend seeing.
Now, as for the point you were trying to make, I can definitely see what you mean, but the point is, Bieber is a large, public name. And no matter how old large public names are, be they music artists, actors, or other celebrities, people are going to fantasize about them, more so if they happen to be attractive and appeal to their particular tastes.
I think the real point I need to make is that, its just a character that you're pointing the finger at, and not even an actual human character, just an alien puppet with a humans voice coming out of it. That is in no way a real person voicing their real opinion, or even someone that is outright saying that they fantasize about Justin Bieber. All in all, I think theres no real reason to be up in arms over this commercial, but that's just me. Seeing as I've never gone to Great Britain, or even really care what people fantasize about, I can't honestly say one way or another if its really wrong or not.