The Cabinet Secretary revealed that in 2020 he was encouraged by a now former member of the No. 10 team to ask the Royal Foundation for a position on the Earthshot Award for Mr Johnson’s then-fiancé.
But Mr Case – who has close links to the Duke of Cambridge, who is his former private secretary – insisted he had not approved her for any paid work.
He admitted in response to a letter from Labor deputy Angela Rayner demanding that he explain his involvement in Mr Johnson’s alleged efforts to secure top jobs for Mrs Johnson – and specifically whether he had approached the Royal Foundation.
In response, Mr Case insisted that there had been “no inappropriate behavior”, saying: “I did not recommend Mrs Johnson for any role.
“In the fall of 2020, a former member of the number 10 team asked about opportunities for Mrs. Johnson with charities.
“I was happy to have an informal conversation with someone involved in the Earthshot Award about what roles were available, as I would have done for anyone with relevant experience who was eager to engage in charity work.”
It comes after the Prime Minister did not reject allegations that he had talked to his aides about environmental roles for his wife in 2020, neither to the Cop26 summit nor to the royals.
It followed reports that when Mr Johnson was Secretary of State in 2018, he was trying to hire Mrs Johnson – then known as the maiden name Symonds – as his chief of staff at £ 100,000 a year while still married to his second wife. Marina Wheeler.
In her letter to Mr Case, Mrs Rayner said the potential conflicts of interest raise “serious issues of sleaze and corruption” in Downing Street.
She wrote: “There are now serious questions that the Prime Minister has to answer about potential inappropriate and conflict of interest in his lobbying for a high-paying tax-funded job for his partner in 2018, Carrie Johnson.
“Reports suggest that while Secretary of State Johnson was trying to get Johnson appointed to a secretary of state job in 2018 and to other roles, including one with a royal charity.”
Mrs Rayner continued: “It is clearly inappropriate for the Prime Minister to be a judge and jury in his own case, so I ask you to confirm that this case will be the subject of an independent inquiry and fully investigated.”
She told Mr Case that she wrote to him “in the absence of an independent adviser on ministerial interests” following Mr Johnson’s independent ethics adviser Lord Geidt’s resignation last week.
Ms Rayner said she was concerned about the “sharp hole in the standard system” after his resignation.
She also wrote separately to Lord Evans, chair of the Committee on Standards in Public Life, urging him to “initiate an independent inquiry into this matter”.
Downing Street said Mr Johnson had never recommended Mrs Johnson for a government role, but stopped denying that he was considering or discussing the move.
The Prime Minister’s official spokesman this week said: “The Prime Minister has never recommended Mrs Johnson for a government role, or one as part of the Earthshot Award.
“Other than that, I would not get into any conversations that the Prime Minister may or may not have had in private.”