THE government's test-and-trace system will launch tomorrow, the prime minister revealed.

Setting out details of the scheme, he told MPs that people contacted by an NHS official and told they had been in contact with someone who had coronavirus would need to self-isolate.

Although the initial scheme would rely on people following the guidance, Mr Johnson said if there was not widespread compliance a system of fines could be introduced to punish those who do not do what they are told.

"We will be asking people to stay at home. If they don't follow that advice, what we will be saying is we will consider what sanctions may be necessary," he said.

The Prime Minister told the Liaison Committee of senior MPs: "To begin with, we're asking people to to do it as a matter of course, if they're contacted by an NHS tracer, and you are told that you have been - for more than 15 minutes - less than two metres away from somebody who has tested positive for coronavirus, then you should self-isolate."

Acknowledging that this would place a burden on a "tiny minority" of people, Mr Johnson said it would help release the rest of the country from lockdown.

"It is a huge imposition, but it will be on a very small minority of the population.

"And I would just say to everybody that it's worth it, because that is the tool that other countries have used to unlock the prison, to make sure that we can go forward.

"And so, that captivity for a tiny minority for a short time will allow us gradually to release 66 million people from the current situation so I do think it's the right way forward."

Health Secretary Matt Hancock described the scheme in more detail at the government's daily briefing. 

It will allow the government to replace a national lockdown with "local action" - instead of locking many people down, isolating a few.

those who have been in contact with symptomatic people will be told to self-isolate, even if they themselves do not have symptoms.

He acknowledges this will be a "big ask" but calls on people to follow the advice for the safety of everyone.

He added that there will be bumps in the road but says the scheme will improve over time.