Lockdown was further eased yesterday, with schools and more non-essential shops reopening.
People who have been shielding for 10 weeks are also allowed outside.
They can now meet one person from a different household as long as it's outside and they stick to social distancing guidelines.
Others can now meet outside in groups of up to six.
It comes as the rate of new daily infections dropped significantly.
At the start of the outbreak the UK was reporting around 6,000 new cases per day.
It has now dropped to less than 2,000, with death rates also falling.
However, the warmer weather combined with lockdown easing has seen Brits heading to the coast en masse.
And there are fresh worries the "R rate" – used to indicate the speed at which the virus is spreading – could start to rise.
This would bring about a possible second spike in infections.
"A really, really critical time"
He said: "We have always said that we are prepared to reintroduce measures – whether that is nationally or in response to a localised outbreak – if that is necessary."
Deputy chief medical officer Jenny Harries added: "This is a really, really critical time. The public really, really need to stick to [government guidelines]."
We have always said we are prepared to reintroduce measures if that is necessary.
She added: "It is not just about what it is possible to do. It's about what it is sensible to do and what is sensible to do is have as few interactions as possible."
Harries continued: "There are plenty of opportunities to go out and exercise, be out in the sun, without being next to other people."
She added: "It's really important that people try to use those measures sensibly for their own benefit, but don't risk transmission with other people."
Test and trace
Matt Hancock also explained that test and trace will play an important part in figuring out where lockdown could be reintroduced in the future.
He said: "We are attempting to move the system from these national, blanket measures to a more targeted approach."
The MP added: "This is why test and trace is such an important part of that."
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