Diners are entitled to a 50 percent discount on food and non-alcoholic drinks to eat or drink in, up to a maximum of 10 pounds ($13) discount per head every Monday, Tuesday and Wednesday between Aug. 3 and Aug 31.
The offer - expected to cost half a billion pounds ($650 million) - is open to diners in participating restaurants, cafés, bars, pubs, work and school canteens and food halls. More than 72,000 restaurants have registered, finance minister Rishi Sunak said.
Matt Healey, 23, who works in digital marketing for Warner Bros., was glad his cooked "English breakfast" would cost him half the usual price at Maggies, a cafe in Lewisham, south-east London.
But he said the priority for him remained the health risks over the discount. "It's a bit of a balancing act," Healey said. "I think the risks will probably outweigh the 50 percent off."