As craft gins have become increasingly popular, tonic sales have topped £116 million, a rise of 37 per cent in the past year.
Shoppers spent an extra £32 million on tonic in the past year, buying an extra 18 million litres.
Trendy mixer brands such as Fever-Tree and Fentiman’s have performed especially well in the past year, said analysts Kantar Worldpanel.
Sales of Fever-Tree grew 65 per cent to £42 million, while Fentiman’s almost doubled its value to more than £5 million.
At the same time, gin sales are up nearly 14 per cent to £381 million, said Kantar.
Trade magazine The Grocer reported: “Corks are literally popping in adult soft drinks, as sales of posh booze alternatives and accompaniments boom.”
Researchers said a rise in the price of tonic averaging 17 per cent had not put off drinkers paying more for their G&T mixers.
Total sales of adult soft drinks are up 14 per cent to £281 million, with tonic taking the lion’s share of the £34 million annual growth.
Saskia Mayer, marketing director of Fever-Tree, told The Grocer: “If a customer is willing to spend money on a quality gin, why then pair it with a poor quality, artificially sweetened tonic that would mask the fantastic botanicals and flavours that went into making it.
“The recent boom of premium and craft spirits, in particular gin, has influenced the mixer market hugely and we firmly believe it is mutually beneficial to both sides.“
Adult soft drinks are increasingly being sold in glass bottles, which gives them a more premium feel, even though they cost nearly 70 pence a litre more than plastic bottles.
Other adult soft drinks which are enjoying a boom in sales include premium colas, ginger beers, elderflower presses and other upmarket tipples as mixers to be served with alcohol.
Some other brands are blurring the boundaries further, using botanicals, herbs and spices to create sophisticated flavours that can be drunk on their own.
Trevor Smith, head of brand marketing for soft drinks at SHS Drinks, said: “Adult soft drinks are fully aligned with major current market trends including premiumisation, less sugar consumption and growth in low and no alcohol drinks, particularly among millennials.
“Adult soft drinks tick all the boxes, putting them in a prime position to capitalise on all these trends.”