Rachel Johnson has said that “all rules were followed” at Chequers amid fresh allegations against her brother of breaking Covid lockdown rules.
Boris Johnson has been referred to police over gatherings he attended in Downing Street and Chequers while prime minister.
Speaking on LBC on Monday night, Ms Johnson said: “If he has questions to answer he will definitely be answering them.
“I see that the family name has been brought into it slightly and all I will say on that point… is that as far as I am aware all the rules were followed whenever I went to Chequers, which wasn’t often enough.”
The referral to police has been branded a political “smear” by Johnson’s allies, while his spokesperson said the allegations against him were "totally untrue".
Supporters of the former prime minister noted that Oliver Dowden, the most senior minister in the Cabinet Office, is one of Rishi Sunak’s closest friends in politics.
But Cabinet Office sources said that no minister was involved in the decision, dismissing any accusation of politicking and saying officials were duty-bound to act.
While little is known about the gatherings at the heart of the latest development, one source familiar with them said there were a "handful" of events. Another said "more than ten".
The police confirmed they occurred between June 2020 and May 2021, a period in which the country moved in and out of lockdown.
A spokesman for Mr Johnson said: "Some abbreviated entries in Mr Johnson’s official diary were queried by the Cabinet Office during preparation for the Covid Inquiry.
"Following an examination of the entries, Mr Johnson’s lawyers wrote to the Cabinet Office and privileges committee explaining that the events were lawful and were not breaches of any Covid regulations."
The spokesman added: "The assertion by the Cabinet Office that there have been further Covid rule breaches is totally untrue.
"No contact was made with Mr Johnson before these incorrect allegations were made both to the police and to the privileges committee. This is both bizarre and unacceptable.
"For whatever political purpose, it is plain that a last-ditch attempt is being made to lengthen the privileges committee investigation as it was coming to a conclusion and to undermine Mr Johnson.”
'Another politically motivated stitch up'
The spokesperson said Mr Johnson’s lawyers have written to the police forces involved to explain in detail why the Cabinet Office is “entirely wrong in its assertions”.
"The events in question were all within the rules either because they were held outdoors or came within another lawful exception. They include regular meetings with civil servants and advisers.
"Many will conclude that this has all the hallmarks of yet another politically motivated stitch up,” they added.
A Cabinet Office spokesman said: "Information came to light during the process of preparing evidence for submission to the Covid Inquiry.
"In line with obligations in the civil service code, this material has been passed to the relevant authorities and it is now a matter for them."
The civil service code states: "In line with the core value of integrity, civil servants must comply with the law and uphold the administration of justice."