Protesters stood outside the British Parliament, while inside Prime Minister Boris Johnson defended his decision to implement the new lockdown, saying the new, more contagious, coronavirus variant offered little choice.
Lawmakers were due to vote on the measures introduced earlier this week, which included shutting schools and shops and ordering citizens to stay at home as a surge in cases of a new coronavirus variant threatens to overwhelm the healthcare system.
Johnson, who has been criticised for being too slow to introduce strict regulations in the first wave of the coronavirus pandemic, is not expected to face a large rebellion from his Conservative Party in the vote on the lockdown. But some in his party are critical of any "draconian" restrictions, demanding that they are removed as quickly as possible.
Britain has been among the countries worst-hit by COVID-19, with the highest death toll in Europe. With the appearance of the new variant, it has seen case numbers repeatedly reach record highs, stretching the country's health service.
Johnson said the legislation would run until March 31.