Boris Johnson's former communications chief threatened to use his contacts in the press to confront the BBC over its coverage of the Conservative mayor of London, suggesting that "good friends in No 10" could also be deployed against them, emails leaked to the Guardian reveal.

The threat of a "huge public fight" was levelled at senior BBC figures by Guto Harri, a former BBC correspondent himself, who announced last week that he was moving to become director of communications at News International.

In the emails, Harri told Will Walden, the BBC's Westminster news editor – whom Johnson has since chosen as Harri's replacement as head of communications at City Hall – that the BBC faced a "huge public fight" if an interview about Johnson with his unauthorised biographer, Sonia Purnell, went ahead.