Boris Johnson and his staff were given compulsory training on the importance of acknowledging personal friendships months before he met the US businesswoman Jennifer Arcuri, and just after he was rebuked for failing to declare an interest with another woman, the Guardian can reveal.

City Hall’s standards committee recommended the governance training after a panel found that Johnson had failed to acknowledge a personal interest in Helen Macintyre. It later emerged that Macintrye, who held an unpaid advisory post, had an extramarital affair with Johnson and gave birth to his daughter in 2008.

According to the panel’s report, in November 2010 the mayor acknowledged that he should have declared an interest and pledged to “bear in mind the definition of close associate in the future”. That decision is now being reviewed by a City Hall watchdog as part of its investigation into allegations that Johnson used his influence to favour Arcuri.

In March 2011, the standards committee agreed to roll out compulsory governance training for “any person covered by the codes and guidance”. Issues to be raised in the training included the importance of registering interests, according to minutes of the meeting at the time.

Six months later, Johnson met Jennifer Arcuri at a gathering of venture capitalists in an encounter she described as “electrifying”. When they met in October 2011 Johnson agreed to speak at the launch of her company, she claimed. He went on speak at four of her company’s events in total, and Johnson’s promotional agency London & Partners gave her £11,500 in sponsorship. She was also given a place on trade missions with the mayor after intervention from his office.

Johnson’s register of interests made no mention of Arcuri and he has since insisted he had no interest to declare. Arcuri has claimed she was given no favours by Johnson but admitted this week that they had “very special relationship”, which she wished he had declared.

Claer Lloyd-Jones, the independent chair of the panel that investigated the Macintyre case in 2010, told the Guardian that Johnson could not plead ignorance about the importance of declaring an interest in his close associates.

Lloyd-Jones stressed that she had not been involved in any of the investigations into Johnson’s relationship with Arcuri, but said: “He cannot rely on failing to understand what ‘close associate’ meant for any future case. It was made very clear to him as part of the Helen Macintyre case.”

She said her recommendation to give governance training to all City Hall staff was in part a response to the Macintyre case. “It was influenced by all cases and the abolition of standards committees by the coalition government. Training represents good practice.”

John Biggs, a former Labour London assembly member who blew the whistle on Johnson’s relationship with Macintyre and prompted the panel’s investigation, said: “I think it is fair to say that he has form on this matter and that he would not be short of impartial officer advice on avoidance of conflict or perceived conflict if he had sought it.”

Biggs, now mayor of the London borough of Tower Hamlets, added that Johnson “could not plausibly claim that he hadn’t been alerted to such a risk of actual or perceived conflict and inappropriate behaviour”.

On Monday the Guardian revealed that the Macintyre investigation will be reviewed by the London assembly’s oversight committee as part of its stalled investigation into Arcuri.

The investigation is on hold while the Independent Office of Police Conduct decides whether there is enough evidence to mount a criminal investigation against Johnson into allegations of misconduct in public office over the alleged favours to Arcuri. It is expected to delay an announcement on its decision until after the election.