But the research, from Nielsen and CGA Strategy, found that the on-trade still makes up 56% of spirits sales by value.
Speaking at the launch of First Drinks' first Market Report on Thursday (July 21), sales director John Hyman said consumers are going out far less than they were six years ago.
"In 2005, 38% of people went out just once a week. Today that is 70%," he said.
First Drinks has identified three key opportunities for spirits sales in the off-trade - gifting, smaller formats and online sales.
Convenience stores are the only off-trade area where drinks sales have fallen, according to the report - and Hyman said smaller formats could be the key to boosting sales in the sector.
He said: "We think the choice of 1-litre bottles is too much in convenience - the cash outlay is too big in premium categories, so bottle formats probably need to be converted to half-bottles. The key going forward is the ultimate range of 50cl and half-bottles, and building a compelling activation programme around that to make the shopping environment more interesting.
"It can be a dull environment behind the counter in convenience stores. Theft is an issue, but there is no excuse for having a dull shopping environment - and I'm sure we can find ways to make it more engaging."
First Drinks Brands managing director Chris Mason said: "We are in a very tough environment - this is probably one of the most challenging market environments we've experienced in the liquor trade in the past 10 years."