Basically the British PM is saying we can't tolerate the actions of Al Assad. It is easy to say that. It is all talk though. The reality is that Russia support these guys. Nobody wants to invade. So we are stuck. Sure. Someone may nut up enough to drop a few bombs, but that won't solve anything. We could also go drop a few humvees and a few companies of infantry and tanks and such. But then it is just a waiting game.
So what are we left with? Arming Al Queda? Certainly not. Syria is a prime example of containment and why the west should stay the hell out of the Middle East. It is only a matter of time till someone kills Assad or ousts him from power. And we all know the rebels are not good guys either in this. People want to know how to solve the Middle East violence problem? Let it runs its course.
The reality is that nobody will support conflict there. People are going to die. A few bombs may be dropped by the "UN" but a few more craters in the Mid East is nothing new.