Boris Johnson says he is "confident" his roadmap out of lockdown won't be slowed down - despite the detection of cases of the Brazillian strain of Covid-19.
And he defended the Government's border quarantine measures, saying they had been introduced "as fast as we could"
The Prime Minister told reporters: "We have got one of the toughest border regimes anywhere in the world for stopping people coming in to this country who may have variants of concern."
And he said a "massive effort" was under way to prevent new coronavirus variants spreading.
Mr Johnson said: "If you look at what we have done in the case of the South African variant, a massive effort went in there.
"The same is going on now to contain any spread of the Brazilian variant."
There was "no reason not to think that our vaccines are effective against these variants of concern at the present time" and Public Health England "don't think that there is a threat to the wider public".

The PM said the Government moved "as fast as we could" with introducing hotel quarantine measures, calling it a "very tough regime".
Asked if the Government was too slow to implement quarantine hotel measures, the Prime Minister told reporters: "I don't think so, we moved as fast as we could to get that going.
"It's a very tough regime - you come here, you immediately get transported to a hotel where you are kept for 10 days, 11 days.
"You have to test on day two, you have to test on day eight, and it's designed to stop the spread of new variants while we continue to roll out the vaccination programme.
"We don't have any reason at the present time to think that our vaccines are ineffective against these new variants of all types."

And he said he still expected the road map for easing England's restrictions would be irreversible.
He said: "What we are doing is embarking now on a journey, a one-way road map to freedom and it is designedly cautious in order to be irreversible.
"That is what we are hoping to achieve. Some people say we should go faster, some people say we should be more hesitant.
"I think we are going at the right pace, education is the priority, getting all schools open on March 8 is something that we have set our hearts on for a long time and I am confident we will be ready."
Mr Johnson defended the testing regime for schools, insisting "people do understand how to use them and we are very confident that they will be of use in helping to keep the disease under control, keep it going down as we get schools back open".