People living under Tier 2 restrictions in England have been warned they can only order alcoholic drinks with a substantial meal, and they cannot order any more once their food is finished.
Under Tier 2 rules pubs can only remain open if they function as restaurants, and people can only purchase alcohol if done so alongside a substantial meal.
Asked how long drinkers can stay in pubs after purchasing a meal, Boris Johnson's spokesman said: "We've been clear that, in Tier 2 I believe, that you need to have a substantial meal if ordering any alcohol."
He said "once the meal is finished, it is at that point" that people should leave the premises.
When England's lockdown ends on December 2, areas will be placed back into coronavirus tiers, with 99% of the country set to be placed into either Tier 2 or 3.
Under stricter Tier 3 restrictions, pubs, bars and restaurants will be limited to takeaway or delivery services.
Tier 1 - which will cover just 1% of England's population - is the only tier which allows people to order alcohol in hospitality venues without the caveat of having to purchase a meal too.
According to the government, over 32 million people in England will live under Tier 2 - 57.25% of the population - and more than 23 million people will live under Tier 3 - 41.48% of the population.
The PM has defended the tough measures, saying they are essential to reduce the spread of coronavirus.He said he was forced to use the tough measures because the incidence of coronavirus is "still really pretty high".
"It's about 1 in 80/85 people in this country have it," he added.
"I totally understand why people are frustrated, I get that."
Pub landlords in Tiers 2 and 3 have hit out at the new restrictions imposed on them, saying they will cause a huge loss in revenue.
Glen Duckett, a landlord in Greater Manchester, said the restrictions are "unnecessarily going to cause hardship", pointing out that the region has seen a fall in the rate of coronavirus infections.
"With the lockdowns plus all of this, going into December which is one of our key trading times, we've lost tens of thousands of pounds and we're a small business, we help disadvantaged young people into work," Mr Duckett said.
"There's just a complete lack of comprehension by the people making the decisions, it's inconsistent, knee-jerk approaches."
Industry groups say they have not been given evidence from the government to justify measures imposed on pubs and restaurants, including a curfew on serving which will be extended to 11pm.
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