Simon Case questioned over role trying to find Carrie Johnson a job | Carrie Johnson

Angela Rayner has challenged Simon Case, the cabinet secretary, about his role in the prime minister’s alleged attempts to secure highly paid jobs for his now-wife, Carrie Johnson.

The deputy labor leader has written to Case, a former private secretary to Prince William, to ask whether he played a personal role in trying to get Carrie Johnson a job at the Prince’s charity, the Royal Foundation, as reported this week.

In her letter, seen by the Guardian, Rayner poses a series of questions to Case, including: “Did the prime minister instruct, request or ask you to discuss the employment of Carrie Johnson with the Royal Foundation?” and: “Will you be referring yourself to the standards commissioner for breaches of the civil service code of conduct?”

She adds: “It is clearly inappropriate that the prime minister should be the judge and jury in his own case, so I ask you to confirm that this matter will be subject to an independent probe and fully investigated.”

Case was handpicked as cabinet secretary by Boris Johnson. He has infuriated some more junior colleagues by escaping a penalty for lockdown-busting parties, despite having to recuse himself from them when it emerged one gathering was held in his office.

Rayner has also written separately to Lord Evans, chair of the Committee on Standards in Public Life, urging him to investigate both that claim over the royal job, and reports, confirmed to the Guardian, that Johnson tried to employ his then-mistress in a senior role in the Foreign Office, in 2018.

Evans’s committee oversees the standards system as a whole and does not usually investigate individual cases – but Rayner points out that after the resignation of the prime minister’s ethics adviser Lord Geidt last week, it is unclear who else would do so.

“In the absence of an ethics adviser, and given it would be appropriate for the prime minister to be the judge and jury in his own case, I ask that you instigate an independent investigation into this matter,” she writes.

Evans, a former head of MI5, recently warned that Johnson risked undermining the public’s trust in ethics in public life. Without an overhaul of the system, including holding the strengthening role that Geidt, he said, “suspicion about the way in which the ministerial code is administered will linger.” Geidt resigned, saying he had been put in an “impossible and odious” position.

Since he stepped down, Geidt has said the prime minister’s apparent effort to hire Carrie Johnson to a taxpayer-funded role four years ago, “could be ripe for investigation”.

Downing Street has suggested it may not hire a direct successor to Geidt, hinting that it could instead hand over the job to a panel, or committee.

In the House of Commons on Wednesday, Johnson noticeably swerved the question of whether he had tried to get Carrie Johnson appointed to a senior post while he was foreign secretary. At the time, he was still married to his second wife, Marina Wheeler.

The Labor MP Chris Elmore asked him: “Has he ever considered the appointment of his current spouse to a government post or to any organization in the working of the royal households? Be honest, prime minister, yes or no?”

Johnson replied: “I know why the opposite party wants to talk about nonexistent jobs … Because they don’t want to talk about what is going on in the real world.” He then went on to discuss employment statistics.