The Prime Minister admitted during a hearing with MPs earlier this month that he had met Mr Lebedev, a former Russian intelligence officer, on the trip.
“It was not a formal meeting, nor something that had been pre-arranged. Officials knew in advance that I was attending the social event,” he wrote to the liaison committee.
“Contrary to some reports, my visit was in line with security protocols established under successive foreign ministers.
“It would not have been normal for officials or security guards to accompany me on such a private and social occasion.”
Mr Johnson acknowledged that ‘any material content should be relayed’ by ministers who ‘find themselves discussing official business without an official presence’.
But he added of his meeting with the two Lebedevs: “It was not necessary in this case. As far as I know, no government business was discussed.
He justified his participation in the rally by citing that Mr Lebedev and his son owned two British newspapers.
“At the time, the Lebedevs’ company owned the Evening Standard and the Independent, as well as the London Live television company.
“His ownership and involvement in the publishing of British newspapers has not been disputed,” he wrote in his letter.
“Leading role” against Russia
Mr Lebedev served in the Soviet Embassy in London in the 1980s and built a fortune in Russia through banking and airlines.
He bought the Independent and Evening Standard newspapers in 2010 before passing ownership to his son.
In a lengthy response to the committee, the Prime Minister also defended his record of playing a ‘leading role’ against Russian aggression and attacked Labour.
“We continue to expose Russia’s malign activities and counter its disinformation tactics” wherever they occur, he said.
He also praised the UK’s role, under his leadership, in helping Ukraine and said sanctions had been imposed on more than 1,000 people with links to the Kremlin.
Mr Johnson stressed that Lord Lebedev ‘expressed his criticism of Putin’s regime’ and that Labor also had ‘considerable engagement’ with him.
Among them were Yvette Cooper, the shadow interior secretary, and Chris Bryant, chairman of the Commons Standards Committee, “both of whom raised the question of my involvement.”