The further easing of lockdown restrictions in England - due to come in this weekend - has been postponed for at least two weeks, amid concerns over an increase in coronavirus cases.
Casinos and bowling alleys will remain shut, with Boris Johnson saying it was time to "squeeze the brake pedal".
Wedding receptions of up to 30 people were meant to be allowed as part of the changes but cannot yet happen.
Face coverings will be mandatory in more indoor settings, such as cinemas.
People attending places of worship will also be required to wear face coverings, in a change that will be applied from next weekend.
But planned changes to guidance for those who have been shielding during the pandemic, and advice for employers, will still go ahead.
Mr Johnson made the comments during a special Downing Street briefing, where he was joined by England's chief medical officer, Prof Chris Whitty.
Prof Whitty warned that it might not be possible to ease the lockdown any further, explaining that the "idea that we can open up everything and keep the virus under control" is wrong.