Corbin & King saw almost 2,000 covers cancel their bookings in the 24-hours after it was announced London would be placed under Tier 2 (high) restrictions.
The capital's move to the higher alert level banned people from different households mixing socially indoors from Saturday.
Writing in the London Evening Standard Corbin & King co-founder Jeremy King reported the group, which operates restaurants including Brasserie Zédel, the Wolseley and Colbert, had seen almost 2,000 covers cancel by lunchtime on Friday, less than a day after the announcement was made.
He said: "I fear deeply for the staff reliant on customers for their income.
"Of course, the impact varies, and while I speak from a 'full-service' restaurateur's point of view, I am acutely aware of the damage this does to the pubs, bars and other venues of the capital that are struggling to survive already, with the government compounding the manifestly stupid ‘curfew' initiative on the grounds of it curbing socialising by limiting drinking and naively believing that people will not wilfully disobey the edicts of tier two and not socialise at all."
King was not alone in reporting the impact of the new restrictions on cancellations, with Jackson Boxer of Orasay in Notting Hill and Brunswick House in Vauxhall writing on social media that 75% of bookings were cancelled this weekend.