Like-for-like sales in pubs, restaurants and bars fell 58% last month as trading slowed dramatically even before the official lockdown on 20 March.
The whole market was hit as guests stayed away as fears about the spread of coronavirus grew. Restaurant groups were down 56.2% compared to March 2019, according to the Coffer Peach Business Tracker, bar chains down 60% and managed pub groups down 57.8%.
Though delivery has been talked up as a possible revenue source, it only accounted for 7.4% of March sales of the 44 companies taking part, up from 5.5% in January.
CGA director said Karl Chessell said: "The drop in sales that began in February and escalated in the next month, meant that even by the end of March, the eating and drinking out sector had fallen into year-on-year decline, down 4.1% on the previous 12 months, with London down 3.7%.
"With shutdown wiping out April sales, apart from a small amount of delivery income, and May likely to be the same, the devastating effect on the market is self-evident. Even if there is an early easing of restrictions, which is far from certain, reopening of the market will almost certainly be phased and gradual. We are looking at a substantial loss of revenue right across the sector."
Paul Newman, head of leisure and hospitality at RSM, added that the data demonstrated that more needed to be done to protect the sector's 3.2 million jobs.
He said: "At a time when cash is so desperately needed to meet the upfront wages for furloughed staff, most operators are still struggling to access the Coronavirus Business Interruption Loan Scheme under current lending criteria. Great uncertainty remains, not only as to the extent of the current shutdown, but also as to what the lifting of lockdown might look like. More support is needed with property-related costs and this includes support for landlords themselves, who remain liable to pay business rates for empty sites."
The data was taken from a smaller sample than usual – some 44 companies – though they still collectively operate over 7,000 sites.