Fell wants to tax some foods and subsidise others because he thinks that people's eating habits and weight are the government's business. I don't agree on principle but I also think his idea is completely unworkable in practice.
I've explained why in a book review for Spiked. Here's a sample...
There are several problems with this, none of which is trivial. Contrary to what you may have heard from quack nutritionists and certain celebrity chefs, food cannot be neatly divided into ‘healthy’ and ‘unhealthy’ categories. Fell acknowledges that defining food as good, bad or indifferent is a challenging prospect, but believes it could be done by creating a citizens’ jury of ‘many hundreds of people, perhaps even thousands’ at a cost of ‘many millions of pounds’. Throwing money at the problem will not solve it, however.
When he talks about ‘unhealthy’ food, he really means ‘fattening’ food – he lives in terror of the obesity ‘epidemic’ – but that is more a question of quantity than intrinsic qualities. Nuts and cheese are high in calories, but are not generally considered to be unhealthy. Orange juice is full of vitamin C, but has more sugar than a coke. Potatoes are not unhealthy, but what if the consumer takes them home and turns them into chips? Is butter better than margarine? Is a bag of salt – which contains no calories but will kill you if you eat it all at once – healthy or unhealthy?
These examples could be multiplied many times over and raise problems that are not going to be resolved by the wisdom of crowds. As registered dieticians tire of having to explain, it is the diet that matters, not individual products.
Do read it all if you're interested.