The UK government has launched the coronavirus track and trace programme amid rumours that it has already crashed and was not ready.
The NHS test and trace service went live on Thursday, in England, with 25,000 contact tracing staff and the capacity to trace the 10,000 contacts per day.
Announcing the new service Matt Hancock said: “As we move to the next stage of our fight against coronavirus, we will be able to replace national lockdowns with individual isolation and, if necessary, local action where there are outbreaks.
The Government did not launch a contact tracing system until now because it needed to flatten the curve of infections first, Mr Hancock said, during Wednesday's Downing Street briefing.
Boris Johnson has acknowledged that being told to self-isolate was a "huge imposition" but people should be aware of why the programme was needed.
And he warned that if the initial voluntary system was not respected, fines could be introduced for people who fail to comply.
The contact tracing app,first trialled on the Isle of Wight, will also form part of the new Test and Trace strategy in the coming weeks.
The capacity for testing will be scaled up, the Health Secretary said, after the launch of the online portal for key workers to order tests in April saw all 5,000 tests booked within two minutes.
Mr Hancock previously aimed for 100,000 tests to be carried out a day in the UK, but this capacity will be expanded to 200,000 per day.
Meanwhile, the test and trace scheme is for England, with Northern Ireland already having a system in place. Health Secretary Matt Hancock said at the daily briefing that authorities were looking at implementing their own test and trace schemes.
Last week the government announced £300m funding for local authorities to support the test and trace service locally, in order to identify and contain local outbreaks in workplaces, care homes or schools.
From Thursday, all symptomatic individuals in England will be able to access a test if they need one. All symptomatic individuals in Wales will be able to book tests from Saturday.
Meanwhile, a further 377 people have died with coronavirus across all settings in the UK, daily figures released on Thursday showed.
The total number of deaths in and outside of hospitals is now 37,837, the Department of Health said.
What is a close contact?
Only people who have been "close" to an infected person will be contacted by tracers and are considered as: people you spend 15 minutes or more with at a distance of less than 2m,
people you have direct contact with - such as sexual partners, household members or people with whom you have had face-to-face conversations at a distance of less than 1m.
The contact must have taken place between two days before and up to seven days after symptoms appeared.
Self-isolate and test
From Thursday, anyone with symptoms including a persistent cough or temperature must self-isolate for at least seven days.
Anyone else in your household should self-isolate for 14 days from when you started having symptoms, as studies have shown people can be asymptomatic for up to two weeks.
If you test positive for the virus you must complete the entire 7-day period of self-isolation.
Once you test positive you will receive a text or email alert from NHS Test and Trace within 24 hours.
This will provide instructions of how to share details of the people you have been in close, recent contact with. This includes your family or other people you live with, as well as people you have been in direct contact with, or within 2 metres of, for more than 15 minutes.
Contain the virus
If someone has been in close contact with an infected person, the NHS Test and Trace service will alert them via text or email.
For those under 18, they will receive a call from the team and a parent or guardian must give permission for the call to continue.
The individual will be asked to isolate for up to 14-days, depending on when they last came into contact with the infected person.