Boris Johnson faces a further headache over the scandal surrounding the funding of his Downing Street flat refurbishment after Labour demanded the findings of an investigation be made public after reports it will exonerate him. Calls for all evidence to be handed over to parliament’s standards commissioner, amid fears of a “Whitehall whitewash”, led to the prime minister trying to prevent the saga spiralling further. Lord Geidt, the independent adviser on interests, is looking into whether he was misled during an initial inquiry in the spring investigating if Johnson knew about payments to cover the redecoration of his flat above No 11. Despite Johnson telling Geidt he knew nothing about donations to fund the makeover until immediately ahead of newspaper reports in February 2021, the Electoral Commission revealed that prime minister had exchanged WhatsApp messages with the donor, Lord Brownlow, in November 2020 about securing further funds. The watchdog imposed a fine of more than £17,000 on the Conservatives for breaching donation reporting laws. On Thursday, the Financial Times said Geidt had exchanged several letters with Johnson and that, while he would criticise the prime minister’s behaviour, he would not change his initial ruling that there had been no wrongdoing. A senior government source confirmed the outcome to the Guardian, and Geidt is expected to publish the letters early in the new year. Angela Rayner, Labour’s deputy leader, said the leak would “only serve to underline the deep flaws in this system”. She called on Geidt to publish his findings immediately and hand the evidence over to Kathryn Stone, the standards commissioner. Stone is said to be considering launching an investigation of her own into whether Johnson broke the MPs’ code of conduct. Evidence Rayner said should be handed over includes WhatsApp messages exchanged between Johnson and the Tory peer who initially covered some the costs of the No 11 refurbishment. A senior Labour source said the prime minister had “made a fool” of Geidt and the outcome of the report showed “you can lie to him and get away with it”. Wendy Chamberlain, the Liberal Democrats’ chief whip, said people deserved “proper answers, not another Whitehall whitewash” and that Johnson was only concerned about “getting himself off the hook”. Tory MPs believed Johnson being exonerated avoided setting off events that could have ended with calls for his resignation if it was found he breached the ministerial code. However, they remained sceptical of whether it was enough to win back the confidence of his disgruntled backbenchers. A minister said: “This is a guy who’s the political equivalent to a cat. He’s been burning through his nine lives and may have got one of them back, but he’s still got very few left. He now needs a period of calm and quiet achievement.” Another frontbencher added of the ill-feeling caused by the scandal: “It’s stuck and it’ll take a lot for the PM to rid himself of the image.” Other senior Tories stressed that regardless of the report’s outcome, they still believed Johnson’s defence was – at best – questionable. One suggested that the prime minister may struggle to “meaningfully regain credibility”. Caroline Slocock, director of the Civil Exchange thinktank and a former private secretary to Margaret Thatcher, told the Guardian that Stone should launch an investigation. She said, comparing the situation to the 1980s political satire: “This looks like classic Yes, Prime Minister – the PM both knew and didn’t know about the funding of his flat and was both open and not open to Lord Geidt by concealing WhatsApp exchanges.” Slocock added the outcome showed “the need for a truly independent adviser on ministerial standards” who was independently appointed and able to investigate breaches of the ministerial code without permission from the prime minister. Dr Catherine Haddon, a senior fellow at the Institute for Government, agreed that Geidt “needs to show he can still be an effective watchdog” by pushing for the report to be published imminently and seeking to gain more powers and independence “so that this situation can never arise again”. She said while Johnson may feel relieved he has been cleared, the “saga of the wallpaper is unlikely to be over”, and that the investigation had “badly damaged the public’s confidence in ministerial code investigations”. The Cabinet Office said it would “not comment on speculation” and pointed to the terms of reference of Geidt’s investigation, which said his advice to the prime minister would be “published in a timely manner”.