Priti Patel has announced new £800 fines from next week for anyone attending an illegal house party of more than 15 people.
The home secretary said the fine will double for each repeat offence to a maximum level of £6,400.
She told a Downing Street press conference: “The science is clear: such irresponsible behaviour poses a significant threat to public health. Not only to those in attendance, but to our wonderful police officers who attend these events to shut them down.”
Boris Johnson has suggested England could stay under lockdown restrictions through the spring and into summer.
The prime minister said it was "too early to say" when asked whether rules could be relaxed in the spring or continue for longer.
His remarks came as scientists said infection levels in England may have risen at the start of January, with swab tests indicating the highest figures were in London.
They also follow an announcement by health secretary Matt Hancock that the NHS is vaccinating people against Covid-19 at a rate of 200 jabs each minute.
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