The study, which tracks data from 37 groups including Gaucho, Byron and YO! Sushi, found overall like-for-like sales rose just 0.2% last month.
Hospitality brands in London fared particularly badly with a 1.6% decline, while the rest of the country saw a 0.8% increase in sales compared to August 2016.
“These numbers reflect the tough summer that many pubs and restaurant businesses have suffered,” says Mark Sheehan, managing director at Coffer Corporate Leisure.
“There is no hiding. These like-for-like figures are well below inflation. For restaurants particularly they reflect the [increase in] new openings that have taken some trade from established operators.”
CGA vice president Peter Martin added that though sales were ‘sluggish and hard fought for’ hospitality was still performing well in the face of rising meat, dairy and egg prices.
“The sector has had to absorb significant cost pressures already this year, particularly around property costs and food inflation - and most operators have passed at least some of that on to consumers through price rises,” says Martin.
“The one positive point is that consumers are still going out to eat and drink...[restaurants] are not suffering the way other parts of the economy are, such as car sales."
Overall August hospitality sales are down on the 0.6% increase recorded in July.
Read Restaurant magazine's 10 tips to combat food price inflation here.