Couples living apart will not be allowed to hook up during lockdown under new rules unless they have formed a support bubble.
Ministers were said to be planning to announce changes to the so-called social bubbles - but tonight's lockdown announcement has dashed the hopes of many couples.
Under current rules, couples who do not live together can only visit each other's home if they have formed a social bubble - but only under some particular conditions.
In England, single adults living alone - or single parents whose children are under 18 - can form a support bubble with one other household.
If, for example, a couple lives in separate shared accommodation, they cannot meet indoors under current restrictions because the social bubbles rules apply only if one of the households is a single one.
Boris Johnson announced plans for a national lockdown for England in a press conference with Chief Medical Officer Professor Chris Whitty and Sir Patrick Vallance.
Subject to Parliamentary approval, the new national lockdown will run from Thursday November 5 until Wednesday December 2.
People will only be allowed to leave home for specific reasons such as education, work if you cannot work from home and for exercise, which you can take as many times a day as you wish.
People can also leave for recreation with their own household, or on their own with one person from another household (a 'one plus one' rule).
Examples of recreation include meeting up with a friend in the park for a walk or to sit on a bench and eat a sandwich. People will not be allowed to meet in homes and gardens.
The stricter measures mean couples who live apart in households with other people will not be able to meet indoors.
Mixing within homes will not be allowed anywhere in the country, except for childcare and essential support purposes, when the lockdown comes into effect at 12.01am on Thursday.
In a gloomy Saturday night broadcast, the Prime Minister insisted the new national lockdown is not the same as the "full scale lockdown" of the spring.
He said: "We will get through this but we must act now to contain this autumn's surge.
"We're not going back to the full scale lockdown of March and April, the measures I've outlined are less restrictive.
"But I'm afraid from Thursday the basic message is the same: Stay at home, protect the NHS and save lives."
Referring to the most recent data which has seen an increase in cases, he said "no responsible Prime Minister can ignore" the rising rates of Covid-19 infections.
Pressure has been mounting on Mr Johnson for several weeks, although he is understood to have been persuaded by new data on NHS capacity and figures released on Friday from the Office for National Statistics suggesting 580,000 people a week are now contracting the virus.