A fresh inquiry has opened into Boris Johnson’s relationship with Jennifer Arcuri after the US businesswoman dramatically agreed to assist officials, paving the way for the prime minister to face possible criminal investigation. Arcuri has formally offered to help the Greater London Authority (GLA) ethics watchdog by allowing it to inspect extracts of her diary entries chronicling her affair with Johnson and agreeing to be questioned for the first time by investigators over the relationship. The contemporaneous diary excerpts, disclosed in the Observer last week by the journalist John Ware, reveal how Johnson allegedly overruled the advice of staff to promote the business interests of Arcuri and win her affections. Arcuri’s decision to cooperate with the GLA monitoring officer reopens the prospect of Johnson facing an investigation for a potential criminal offence of misconduct in public office. In a previous investigation into Johnson’s business relationship with the then 27-year-old Arcuri, the Independent Office for Police Conduct (IOPC) did not have access to Arcuri’s handwritten diary entries in which she made “verbatim” notes of the highlights of his telephone calls and their conversations. The police watchdog eventually concluded it would not be launching a criminal inquiry into whether Johnson abused his position as London mayor to “benefit and reward” Arcuri. Investigators also never interviewed Arcuri or received testimony from the tech entrepreneur. Her evidence is potentially even more critical because the original IOPC inquiry was also hampered by the deletion of key email and phone records at City Hall that prevented the watchdog from “reviewing relevant evidence”. The latest developments into allegations that Johnson offered to help Arcuri launch her tech business while simultaneously pursuing her for sex will pile more pressure on the prime minister, raising fresh questions over his integrity and lax approach to probity in public life after weeks of sleaze allegations have engulfed his party. After the Observer last week revealed some of the explosive entries in Arcuri’s diaries, Labour’s deputy leader, Angela Rayner, wrote to the GLA’s monitoring officer, Emma Strain, asking that she urgently refer the new evidence to the IOPC to “look again” at its decision to rule out a criminal investigation. Strain, in turn, contacted the Observer for assistance in obtaining Arcuri’s diaries so she could assess whether the issue was a “serious complaint” that appeared to constitute or involve a criminal offence being committed. If Strain judges that the issue is serious, she will formally refer the matter back to the IOPC to decide if it will investigate Johnson over the criminal offence of misconduct in public office. After several days of weighing up whether she wanted to assist the GLA, Arcuri finally agreed and at 7pm on Friday sent an email to Strain, head of its ethics watchdog. “I am prepared to show you or your investigators copies of the relevant pages,” Arcuri wrote. “However, I currently reside in the United States, so it would mean you or they [the IOPC] travelling here for that purpose. In that event, I would also be prepared to be interviewed, if that assists.” If that is not possible, Arcuri has authorised veteran journalist Ware, with whom she has “entrusted” her diaries, to show investigators relevant pages detailing her business dealings with Johnson. Arcuri handed the first tranche of her diaries to Ware after the 2019 general election and following his ITV documentary in which he accused the prime minister of having a “tenuous relationship to the truth” after Johnson’s repeated insistence that “absolutely everything was done with full propriety” regarding his relationship with Arcuri. Ware was sent a second tranche of material from Arcuri in May 2020.Ware approached Arcuri after recent comments by Johnson about public probity and she consented to allow publication of some of her diary extracts. One Arcuri diary entry reveals how Johnson offered to be her “throttle” in an attempt to accelerate her business career, claims that may reopen the possibility of Johnson facing a potential criminal investigation into misconduct allegations. It recalled how Johnson told her: “How can I be the thrust – the throttle – your mere footstep as you make your career? Tell me: how I can help you?” The diary entries also suggest that Johnson broke the rules governing ethical conduct in public office in his dealings with Arcuri. Responding to the Arcuri revelations last week, a government spokesperson said: “As mayor, Boris Johnson followed all the legal requirements in the Greater London Assembly’s [sic] code of conduct at the time.”