The former top Foreign Office civil servant has acknowledged revealing to colleagues – including government ministers – that he voted to remain in the EU during the 2016 referendum. Simon McDonald said he was speaking to colleagues shocked at the result in an effort to maintain credibility by stressing they must deliver the government’s policies, regardless of their personal views. He made the admission in a documentary by the BBC’s Laura Kuenssberg on the chaos that has reigned in UK politics since 2016. The show, which airs on Monday, also confirms conversations within government suggesting the former deputy prime minister Sir David Lidington could have replaced Theresa May in No 10 to offer a second referendum on leaving the EU. Lord McDonald is a controversial character among some Conservative Brexiters and played a role in the downfall of Boris Johnson after leaving office. He told the BBC the main feeling in the Foreign Office after the 2016 referendum was of “mourning”, adding: “People were in tears. People were in shock. On this occasion, this solitary occasion, I decided to tell my colleagues and, therefore, let ministers know that I voted to remain in the European Union.” The code for civil servants requires them to act with impartiality by never allowing “personal political views to determine any advice you give or your actions”. It does not preclude holding a view that runs contrary to the government of the day. McDonald, who was the Foreign Office’s permanent secretary between 2015 and 2020, said he believed colleagues knew his position anyway. “I was trying to maintain credibility and trying to convey a message to a group of people, most of whom I felt had voted to remain in the EU, that their personal feelings were beside the professional point,” he added. He acknowledged the Foreign Office board was “not entirely comfortable” with the move. The former deputy cabinet secretary Helen MacNamara responded: “Wow … I don’t know why that would be a good or helpful thing.” McDonald played a role in Johnson’s downfall as prime minister by revealing that he had been warned about a complaint against Chris Pincher before appointing him as a party whip. Johnson was facing claims he had lied about how he had dealt with Pincher’s case. He publicly claimed not to have known of prior specific allegations, but McDonald wrote to the parliamentary standards commissioner to say the then prime minister was briefed in person about a 2019 complaint of alleged groping. Johnson subsequently agreed to go after his handling of the scandal led to a torrent of resignations by ministers and mounting pressure from within his own party. Later in the documentary, Lidington confirms that the possibility of him taking over as prime minister to call a second referendum was discussed as May struggled to get her Brexit deal through parliament. “Yes, that was what happened,” he said, before downplaying the likelihood of it happening. “Theresa was not going to go, that was very clear. And I certainly never made any suggestion to her or made any move against her. I would not have done so.” Laura Kuenssberg: State Of Chaos is being broadcast on BBC2 at 9pm.