The British people must avoid non-essential contact and stop all unnecessary travel, UK Prime Minister Boris Johnson warned after receiving advice that coronavirus cases could double every five days.
Speaking at a press conference on Tuesday, Johnson said that the country was entering a "fast-growth" period, where the number of COVID-19 cases recorded could double every five days without "drastic action". There have so far been 1550 cases reported in the country, with 53 deaths.
In order to combat that rapid spread, the Prime Minister said anyone with symptoms, or within a household where someone has symptoms, should isolate for 14 days. They should not leave the house for food or essentials, unless they have no other way to get them.
Johnson said even if someone doesn't have symptoms, all non-essential contact should be ceased, as should all unnecessary travel. He has called for people to work from home and avoid pubs, clubs and theatres.
The UK Government will also no longer support mass gatherings using emergency workers.
"Mass gatherings, we are now moving emphatically away from," he said.
These new measures could last for months, with authorities focussed on the "long game".
The country's chief scientific adviser Sir Patrick Vallance says school closures may be necessary, but only at the "right time".
It will be necessary to go even further from this weekend, Johnson warned. He said people with serious health conditions should be "largely shielded from social contact" for around 12 weeks.
Those over the age of 70 are of the greatest focus for the UK Government. It has previously mooted requiring all those over 70 to self-isolate for months. All MPs over the age of 70 won't be allowed in Parliament.
The Prime Minister wants to ensure that the most critical measures are being undertaken during the virus' peak time, which he says may still be weeks away. He said these measures are "overwhelmingly worth it to slow the spread of the disease, to reduce the peak, to save life, minimise suffering and to give our NHS the chance to cope".
The UK's objective is to "suppress" the curve in order to keep it below the health system's capacity. Sir Patrick has previously said authorities wanted to build up herd immunity.
"Because the vast majority of people get a mild illness, to build up some kind of herd immunity so more people are immune to this disease and we reduce the transmission, at the same time we protect those who are most vulnerable to it."
The plan to increase herd immunity has frustrated some experts. New Zealand microbiologist Siouxsie Wiles said it was a flawed strategy.
"It's a vaccination strategy - it's not a disease strategy. It's really amazing they're going to use that - basically just let everyone get infected and hopefully the older and more vulnerable people will be protected - it's insane," she told The AM Show.
If the health system is at capacity dealing with COVID-19 patients - some of whom will require hospitalisation for six weeks - others will miss out, she says.
"The worry is if we let this go through, we won't have enough hospital beds, we won't have enough intensive care beds and we won't have enough ventilators. That means if you have a car accident or a stroke, we won't be able to care for you either.
"This is what's happening in Italy. Doctors are having to decide who gets treatment."
There have been more than 175,000 confirmed cases worldwide. The United States is banning anyone entering the country if they have been to Europe in the last 14 days.
The World Health Organization on Tuesday said this was the "global health crisis of our time".
"We have seen a rapid escalation in social distancing measures, like closing schools and cancelling sporting events and other gatherings," WHO Director-General Dr Tedros Adhanom Ghebreyesu warned.
"But we haven't seen an urgent enough escalation in testing, isolation and contact tracing, which is the backbone of the COVID-19 response."
