Warning of "difficult months to come", British Prime Minister Boris Johnson imposed fresh restrictions on the movement of people and economic activities in the country, in a bid to bring under control a new wave of coronavirus infections.
Mr Johnson also warned of "even tougher measures" in the weeks to come if people do not follow the new restrictions.
Confronted with statistics indicating that climbing infection figures are now beginning to translate into an ominous rise in the number of deaths, Mr Johnson used a rare speech to the nation to reverse his government's previous policy of encouraging people to go back to their workplaces, and is now advising them to work from home instead.
But this move, as well as a raft of other restrictive measures which come into effect today, stop short of the total national lockdown which the British government imposed in March, when the infections first reached a peak.
Mr Johnson is still keen to avoid inflicting further pain on the British economy.
His objective is to save lives, as well as people's livelihoods, a balancing act which his critics warn still risks missing both objectives.
Britain is facing a trend encountered in most European countries - a steep rise in infections, largely driven by younger people who see the virus as no threat to them, and therefore ignore basic hygiene or social distancing measures.
New Covid-19 infections in Britain are growing at about the same pace as they were at the beginning of April, and now run at more than 4,000 detected new cases each day.
For the moment, the number of registered daily deaths is still within the lower teens.
But, as Mr Johnson told his people, "if you let the virus rip through the rest of the population, it would inevitably find its way through to the elderly as well, and in much greater numbers".
"The tragic reality of having Covid-19 is that your mild cough can be someone else's death knell," added Mr Johnson, whose own life was once endangered by the virus infection.
Apart from the advice to work from home, the measures starting today entail an extension of the mandatory use of face masks, a cap of 15 people allowed to attend wedding ceremonies and other public events, as well as instructions to all pubs, bars and restaurants to close by 10pm.
The move to curtail restaurant and bar hours, as well as the new requirement on the hospitality sector that customers should be served only while seated at tables, are intended to prevent the crowding which generally takes place in late evening at various drinking and eating outlets, a dangerous source of infection.
The British government is also tightening penalties for those flouting rules.
Fines for breaches of health regulations can now run up to £10,000 (S$17,400).
The British army has been ordered to stand by for deployment, to allow the police to be diverted to enforce anti-pandemic measures.
Mr Johnson also hinted at the possibility of a complete national lockdown in the next few weeks, should this become necessary, a plan which British ministers refer to - copying a term first used in Singapore - as a potential "circuit breaker".
Schools and universities may close too, if required.
An outbreak of infections at the University of Liverpool in north-west England is particularly worrying for the authorities.
Mr Johnson enjoys cross-party parliamentary support for his measures, as well as the cooperation of the autonomous governments in Scotland and Wales, which have great latitude over their own health policies.
But he is facing criticism from the opposition Labour Party for his government's failure to introduce adequate tracing mechanisms, and for his officials' botched attempts to expand mass testing.
A second coronavirus lockdown, claims Labour leader Keir Starmer, "would be a government failure - not an act of God".
Much will depend on developments over the next few weeks.
Mr Johnson told the British public: "We will spare no effort in developing vaccines, treatments and new forms of mass testing, but unless we palpably make progress, we should assume that the restrictions I have announced will remain in place for perhaps six months."
And, at least for the moment, voters appear to be giving him the benefit of the doubt.
Opinion polls indicate that around 70 per cent of the public support the new measures, with 45 per cent thinking they do not go far enough and just 13 per cent saying they are too strict.