The news media call it “freedom day,” the fast approaching moment when England’s remaining coronavirus restrictions are scheduled to be cast off at last, allowing pubs to fill to capacity, nightclubs to open their doors and the curtain to rise in theaters around the country.

But a recent spike in cases of the highly transmissible coronavirus variant called Delta has prompted such alarm among scientists and health professionals that the country now seems destined to wait a little longer for its liberty.

For Prime Minister Boris Johnson, oft accused of doing too little, too late to combat the virus, the stakes are high. The question is not so much whether to postpone “freedom day” — June 21 — but to what degree. Four weeks seems to be the maximum under consideration, with some advocating going ahead with a limited version of the full opening and others favoring a two-week delay.

An announcement on the next steps is scheduled for Monday, and Mr. Johnson plans to study the data through the weekend. But many health professionals have already made up their minds over the seriousness of the threat from the Delta variant, first detected in India.

“Covid is not going to disappear on the 21st of June, and lifting all measures as early as the 21st risks reversing the significant progress we have made,” said Jim McManus, vice president of the Association of Directors of Public Health, which represents senior health officials around the country.

He called for the extension of the current restrictions “to prevent a further uptick in cases — particularly in areas experiencing high or enduring transmission — and allow time for more people to be vaccinated and protected against the Delta variant.”

Still, the decision encapsulates a dilemma familiar to Mr. Johnson, an instinctive libertarian whose reluctance to take tough measures has been blamed by critics for the country’s high number of Covid-19 fatalities. He has been accused of postponing lockdowns, vacillating over border controls and overruling scientific advice.