Liz Truss has been accused of “running scared” of scrutiny after pulling out of a BBC interview scheduled for Tuesday, meaning she is likely to become prime minister without undergoing a single set-piece broadcast quizzing.

Earlier this month the foreign secretary agreed to a primetime interview with the veteran political journalist Nick Robinson on BBC One, something already done by Rishi Sunak, her rival to succeed Boris Johnson as Conservative party leader.

But a BBC spokesperson said Truss had now cancelled the interview. “Ms Truss’s team say she can no longer spare the time to appear on Our Next Prime Minister,” they said. “We regret that it has not been possible to do an in-depth interview with both candidates despite having reached agreement to do so.”

In a tweet, Robinson said he had been pleased that Truss had agreed to the interview and he was “disappointed and frustrated it’s been cancelled”.

A source in Sunak’s campaign said their tally showed Truss had done just two broadcast interviews of any form during the campaign, whereas Sunak had undertaken nine, also including three spots on BBC Radio 4’s Today programme and an appearance on ITV’s This Morning.

The source said: “It’s important that candidates face proper scrutiny so that members and the public know what they are offering. Avoiding that scrutiny suggests either Truss doesn’t have a plan at all or the plan she has falls far short of the challenges we face this winter.”

Wendy Chamberlain, the Liberal Democrats’ chief whip, said: “Liz Truss is running scared of the media and proper public scrutiny. How can she lead our country through an economic crisis when she can’t even cope with a basic media interview?

“She wants to follow in Margaret Thatcher’s footsteps but she’s fallen at the first hurdle. She’s fighting for the highest office by answering the lowest number of difficult questions.”

Labour also criticised Truss for backing out. Conor McGinn, the shadow minister without portfolio, said: “The British public don’t get a say in choosing the next Tory prime minister and now it seems Liz Truss wants to avoid any public scrutiny whatsoever.

“People will rightly conclude that she doesn’t want to answer questions about her plans for the country because she simply hasn’t got any serious answers to the big challenges facing our country.”

Truss’s tactic of avoiding scrutiny mirrors that of Boris Johnson, who before the Conservative victory in the December 2019 general election declined a BBC interview with Andrew Neil, something faced by rivals including the then Labour leader, Jeremy Corbyn.

Truss has appeared at a series of Conservative hustings events around the UK in recent weeks and faced some difficult questions from the various hosts, although less so from the audiences made up of party members.

But longer-form interviews, in which a candidate can be pushed repeatedly on their answers, are viewed as considerably more difficult.

During some hustings events, Truss has been critical of the media, and of the BBC specifically, accusing some outlets of trying to “talk our country down” and having a leftwing bias.

Truss’s campaign was contacted for comment.