I'm probably in the minority here, but I don't think obesity has a lot to do with advertising, poverty or education.
I think it is a mental health issue and the question shouldn't be about how do we cut down on junk food but more focused on why people are choosing to eat to excess/unhealthily on an ever increasing scale in the first place.
Lets not be daft, even if you're thick or poor you know that a plate full of junk food swilled down with fizzy pop is unhealthy, yet it doesn't put many people off. We need to be asking why people are choosing to put themselves at risk of serious health conditions or completely not caring about their health at all, that is a mental health problem in my opinion. I think large swathes of the country are self medicating with comfort eating and drinking due to various levels of depression/unhappiness.