More than 45,000 people have signed a petition calling for the BBC Trust to “safeguard” the corporation’s independence when it hires the next director general.

Hosted by online campaign community 38 Degrees, the petition comes on the back of comments made by Mayor of London Boris Johnson that to counter-balance what he described as a left-wing bias “we need a Tory, and no mucking around”.

The petition states: “The BBC’s reputation for independence has earned it respect all over the world. But now some outspoken politicians have suggested the job should go to a candidate who is party political.

“If enough of us add our names to an open letter to the Trustees, we can remind them that the BBC should be protected from party political game playing. Add your name to the open letter to the BBC Trustees, telling them to defend the BBC’s independence.”

It is endorsed by trade union Bectu, which condemned Johnson’s comments during its annual conference after an emergency proposition was tabled.

The union said delegates had given “their unanimous support” to the proposition, damning the mayor’s “attempt to interfere in the appointment process”.

A decision about who the new head of the BBC is expected to be made shortly, with some reports predicting an announcement will be made this week.

Likely candidates include Ofcom chief executive Ed Richards – who has acted as an adviser to both Tony Blair and Gordon Brown – as well as internal applicants such as director of Vision George Entwistle, director of news Helen Boaden, chief operating officer Caroline Thomson and director of Audio & Music Tim Davie.