France will be closing all educational institutions, while a "state of emergency" has been announced in New York City, as nations steady for an additional increase in coronavirus cases.
Asked if there is a fear that clamping down too hard on its spread could see it return, Sir Patrick said: 'That is exactly the risk you would expect from previous epidemics.
Britain was on a trajectory of cases "about four weeks" behind Italy and other worst-hit countries in Europe, he added. This is the largest jump in cases so far in one day across the United Kingdom since the coronavirus outbreak started in the UK.
"Many more families are going to lose loved ones before their time", he told a news conference at his Downing Street office.
Boris Johnson has said that anyone with certain symptoms (a persistent cough or fever) should self-isolate for seven days.
School trips overseas should be stopped, people over 70 with serious medical conditions are being told not to go on cruises, and officials warned the advice is likely to develop so that entire households could be told to self-isolate.
Lowering the peak by an estimated 20% by stretching it over a longer period would mean "more beds and more time for medical research ... so society is better able to cope", Johnson added.
"This is now not just an attempt to contain the disease as far as possible but to delay its spread", he said at a news conference with the government's top scientific and medical advisers.
The banning of public events, such as sports fixtures, is still being "considered".
Washington State could see explosion in coronavirus cases, study says
The nine cases include four tied to a suburban Seattle care facility that has reported multiple virus cases and deaths. In Oregon, the state Health Authority said Sunday that a second person in the state tested positive for the virus.
Self-isolating is the advice now being given to people who have recently returned from affected countries or have been in close contact with a person who has tested positive for the virus.
Mr Johnson said the government was "considering the question of banning major sporting events".
Instead, the British premier insisted he would be guided by his scientific advisers, even after some accusations of "complacency" in the government response.
All school trips overseas have been banned.
The Government said it would not move to close schools yet as the evidence for its effectiveness is lacking, though this will be kept under review.
Separately, Scotland's First Minister Nicola Sturgeon said the devolved administration in Edinburgh would recommend banning mass gatherings, including football and rugby, from Monday.
The emergency legislation will also include sick pay for quarantined workers from day one and steps to allow more witnesses in court cases to appear via videolink.
The World Health Organization (WHO) has now categorised the deadly coronavirus outbreak as a global pandemic.