The sugar tax will be an arbitrary burden on the poor which takes no account of the actual make-up of drinks, critics have warned.
The TaxPayers' Alliance (TPA) said some beverages laden with sugar will be exempt from the levy.
The TPA insists the Budget measure should be junked after it carried out a comparison of 49 different drinks across three areas, fizzy and energy drinks that will be taxed, and milk-based ones, and coffees, that will not.
The survey found that Coca-Cola, with 10.6 grams of sugar per 100 millilitres, will be subject to the levy, but a Starbucks signature hot chocolate with whipped cream with coconut milk, which has 11 grams of sugar per 100 millilitres, will not.
The study also noted energy drinks such as Monster Ori.gin, 11g/100ml, will be taxed, but Tesco chocolate flavoured milk, 12.4g/100ml, will not be.
In all, the 10 most sugary drinks analysed by the TPA will not be subject to the tax.
TPA chief executive Jonathan Isaby said: "It is deeply concerning that the Government has given in to the pressures from the public health lobby and is pushing ahead with this regressive tax which will hit the poorest families hardest.
"The evidence shows that the sugar tax has nothing to do with the sugar content of products, so it is farcical to suggest that this will have any positive impact on people's diet or lifestyle choices.
"This is yet another example of irresponsible meddling from the high priests of the nanny state, introducing entirely unnecessary complications into an already complicated tax system and pushing up the cost of everyday products for hard-pressed families."
A Treasury spokesman said: "The soft drinks industry levy is a major step forward in our efforts to tackle childhood obesity. Treating obesity and its consequences costs the taxpayer £5.1 billion every year.
"The levy will be charged on soft drinks because they are the main source of added sugar in children's and teenagers' diets, many with no intrinsic nutritional value.
"Health experts agree there is a specific problem with sugar-laden fizzy drinks that must be addressed.
"One can of cola can contain nine teaspoons of sugar, well over the recommended daily limit for our children.
"The money from the levy will go towards funding more school sport, and expanding school breakfast clubs.
"The levy is designed so that producers don't have to pass the tax on to consumers and if they change their product mix to reduce sugar content, then they will pay less or no tax."