The planned sugar tax will “hit poorest families hardest” and has nothing to do with the sugar content of products, according to the Taxpayers’ Alliance (TPA).

The TPA, which wants the levy to be axed, tested 49 drinks and found that some coffee shop drinks contained more sugar than Coca-Cola, but would not be taxed.

The Treasury said soft drinks would be taxed because they were the main source of added sugar in children’s diets.

The Taxpayers’ Alliance (TPA) survey found that Coca-Cola, with 10.6g of sugar per 100ml, would be subject to the levy, but a Starbucks signature hot chocolate with whipped cream and coconut milk, which has 11g of sugar per 100ml, would not.

The study also noted that energy drinks such as Monster Origin (11g of sugar per 100ml), would be taxed, but Tesco chocolate flavoured milk, (12.4g/100ml), would not be.

The TPA said the sugar tax would be an arbitrary burden on the poor, as it is targeting fizzy drinks, which are disproportionately consumed by lower socioeconomic groups. Overall, the 10 most sugary drinks analysed by the group, which campaigns for lower taxes, will not be subject to the levy.

Jonathan Isaby, chief executive of the TPA, said it was “deeply concerning” that the government was “pushing ahead with this regressive tax which will hit the poorest families hardest”.

Isaby said: “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.”

Last month the recently-announced levy on fizzy drinks edged closer to the bakery sector, as it could soon affect cereals and snacks, according to a government health minister.