So, the Prime Minister is "seriously considering a food levy to tackle Britain's obesity crisis". Give it a rest, Dave. This is a smokescreen everyone can see through. We'd prefer you to get the country off its backside first, then worry about our figures.  anyway, Prime Minister, I know it's the conker season but this is a very gnarled chestnut you're trying to play with. Four years ago, the Labour health secretary, alan Johnson, put it forcefully: "Obesity could be as big a crisis" - there's that "c" word again - "as climate change, unless the nation starts to lose weight soon."  at the time, some thinking people wondered how an increasing number of fat people could threaten all life on the planet. Perhaps, they speculated, heavier people have a deeper carbon footprint? Could the increase in weight make Earth fall out of it