"We need to suppress the virus now," Johnson said in a televised address. "Unless we take action the risk is that we will have to go for tougher measures later."
He also urged people to abide by the new rules, which he outlined to parliament earlier.
"This way we can keep people in work, we can keep our shops and our schools open, and we can keep our country moving forward while we work together to suppress the virus," Johnson said.
BORIS JOHNSON: And to those who say we don't need this stuff and we should leave people to take their own risks, I say these risks are not our own. The tragic reality of having COVID is that your mild cough can be someone else's death knell.
And as for the suggestion that we should simply lock up the elderly and the vulnerable, with all the suffering that would entail, I must tell you that this is just not realistic. Because 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.
That's why we need to suppress the virus now. And as for that minority who may continue to flout the rules, we will enforce those rules with tougher penalties and fines of up to 10,000 pounds. We will put more police out on the streets and use the army to backfill if necessary.
And of course, I'm deeply spiritually reluctant to make any of these impositions or infringe anyone's freedom. But unless we take action, the risk is that we will have to go for tougher measures later, when the deaths have already mounted and we have a huge caseload of infection such as we had in the spring.
We must take action now, because a stitch in time saves nine. And this way, we can keep people in work. We can keep our shops and our schools open. And we can keep our country moving forward while we work together to suppress the virus.