Boris Johnson and his wife Carrie complied with coronavirus rules when a family friend stayed with them over Christmas, Downing Street said.
Nimco Ali reportedly spent Christmas at No 10, despite London being placed under Tier 4 lockdown restrictions in December 2020, preventing most households mixing.
Ms Ali is understood to have stayed with the Johnsons, who at the time were engaged to be married, under the “bubble” arrangements, which allowed friends or family to provide informal childcare – the couple’s son Wilfred was eight months old at the time.
Mr Johnson’s official spokesman said: “The Prime Minister and Mrs Johnson have followed the coronavirus rules at all times.”
Ms Ali insisted “I did not break any rules”, after a report in the US, in Harper’s Magazine, claimed she “spent Christmas with the couple at No 10 despite pandemic restrictions on holiday gatherings”.
The “childcare bubble” rules were open to anyone living in a household with a child aged under 14, allowing friends or family from one other household to provide help looking after the child.
The Prime Minister’s official spokesman refused to confirm whether Ms Ali joined the Johnsons in No 10.
But he added: “The rules made clear you can continue to use a childcare bubble on Christmas itself, including in a Tier 4 area. The Prime Minister and Mrs Johnson adhered to those rules at all times.”
Ms Ali is a longstanding friend of Mrs Johnson’s and a campaigner on issues including tackling female genital mutilation.
She is an independent government adviser on tackling violence against women and girls.