British Prime Minister Boris Johnson is self-isolating after coming into contact with someone who tested positive for Covid-19, a fresh setback after infighting amongst his top advisers plunged Downing Street into chaos last week.

Johnson, who was admitted to hospital with the novel coronavirus earlier this year, is well and does not have any symptoms of Covid-19, a spokesman for the prime minister said.

"He will carry on working from Downing Street, including on leading the government’s response to the coronavirus pandemic," the spokesman said. "The prime minister will follow the rules and is self-isolating."

Johnson met a group of lawmakers in Downing Street on Thursday that included Lee Anderson, a Conservative Party member who subsequently developed Covid-19 symptoms and has tested positive.

The British leader had been hoping to seize back the initiative after last week's drama in Downing Street.

Johnson's office said on Friday that Dominic Cummings, the prime minister's most powerful adviser and a fellow veteran of the Brexit referendum, will stop working for him next month.

Negotiations with Brussels over a post-Brexit trade deal are reaching a climax ahead of the December 31 expiry of Britain's transition period with the European Union.

Johnson also has to decide his next move on England's coronavirus restrictions after he ordered a four-week lockdown that is due to end on December 2. (Reuters)