I've got to agree with Geezer sp. I'm five foot eleven and weigh 13st - my BMI is 25.42, which in English is overweight (albeit only by 0.42).
My 'ideal' weight is between about 10 and 11.5 stone - if i managed to get down to 11.5 I'd look sick!
I don't see why there can't be a fat tax - the taxes on booze and fags may not stop people drinking and smoking, but the revenue produced does help to pay for the NHS - in fact, I seem to recall reading somewhere that the revenue raised from smokers is greater than it costs to treat smoking related diseases.
Obesity related diseases are just as self-inflicted as smoking and drinking related diseases, but for some bizarre reason fat people are considered victims - fat people, as a rule, are lazy overeaters (yes I know some people have medical problems which make them fat, but most do not), and therefore whilst slapping a tax on KFC/Greggs/McShite etc... won't solve the obesity issue, at least the reveune raised will go on to help pay for obesity related diseases.