Honestly, I don't see a problem here.
I mean, legally there may be a problem - I'm not a lawyer, and I'm certainly not overly familiar with British law, so I don't know one way or the other whether such taunts might constitute a criminal offense - though I can say that if that were the case, that law needs to be changed IMO.
Certainly such taunting was in bad taste. But nobody put that kid up on the bridge, and nobody kicked his legs out from under him. I see two possibilities:
First, the kid intended to end his life. In this case, the kid succeeded in his goal. While we might find that goal reprehensible, even morally disgusting, the taunters committed no infraction against the kid in question - indeed, they offered encouragement. Again, certainly they committed an infraction against decorum, possibly against the law, but certainly not against the kid himself.
Second, the kid got up there in order to draw attention to himself, not really intending to take his own life. But then why did he jump? Was he merely complying with the crowd's demands? That seems ridiculous, to me at least. No, if it were truly the case that the kid didn't intend to jump, then the only possibility that I can see as to why he actually did jump is that he saw death as a preferable alternative to the embarassment of getting down and facing that crowd. While such a vain person doesn't deserve death, the crowd didn't force it upon him - he chose of his own volition to jump rather than face the music.
I suppose a third possibility is that rather than actually jumping, he slipped and fell to his death. Again, in this case, I don't see how the crowd is at fault - the kid decided on his own to get up there in the first place.