Gatherings of more than six are being banned to try to halt a second wave of coronavirus.
In his first reversal of the easing of national lockdown, Boris Johnson last night warned a surge in cases must not be allowed to get out of control.
From Monday it will be illegal to assemble in groups of seven or more anywhere in England, whether indoors or out.
The 'rule of six' is a dramatic reduction on the limit of 30 put in place on July 4.
Police will be encouraged to break up larger groups and issue £100 fines, which will then double on each repeat offence up to £3,200.
Only schools, workplaces and a limited number of other locations will be exempt.
Announcing the new restrictions, Mr Johnson said: 'We need to act now to stop the virus spreading. So we are simplifying and strengthening the rules on social contact – making them easier to understand and for the police to enforce.