But the law came under fresh scrutiny when it was disclosed that MPs, Lords and parliamentary staff could legally continue drinking past the deadline in the Palace of Westminster because its establishments are classed as workplace canteens.
The regulations, announced by Boris Johnson last week (watch the Prime Minister doing so in the video below), include exemptions that "workplace canteens may remain open where there is no practical alternative for staff at that workplace to obtain food".
After the decision to keep the bars open came in for cross-party criticism, Parliament announced a change with immediate effect. A spokesman said: "Alcohol will not be sold after 10pm anywhere on the parliamentary estate."
Catering facilities will, however, continue to serve food after the deadline when the House is sitting. Despite being in the centre of London, there are relatively few shops surrounding Parliament – particularly ones that open late at night – and politicians and staff tend to eat on site.
The curfew came into force in England on Thursday, but parliamentary proceedings have not gone on past 10pm which means the exemption has not been used so far.
The Commons Speaker, Sir Lindsay Hoyle, is understood to have made the decision not to serve alcohol in any Commons bars last week, but the rule was clarified on Monday because that was the first day on which the proceedings are likely to run past 10pm.
Health minister Helen Whately had said she had been unaware that the curfew did not apply to Parliament and seemed unimpressed. "We in Parliament shouldn't be sitting round late at night drinking. We have got a job to do when we are there," she told BBC Radio 4's Today programme.