Labour has expressed concerns about the BBC’s political coverage after it was revealed that Boris Johnson has still not confirmed whether he will subject himself to a cross-examination by Andrew Neil.

Jeremy Corbyn’s team agreed to take part in the series of one-on-one interviews with the journalist after the BBC told them the prime minister would definitely be doing a similar broadcast next week. However, a BBC source strongly denied they had told Labour that Johnson had confirmed.

The BBC has yet to confirm the date of Johnson’s appearance, leading to Labour concerns that Johnson could be tempted to sidestep scrutiny from one of the broadcaster’s leading political interviewers.

“For those asking when Boris Johnson’s interview will take place, we’re in ongoing discussions with his team but we haven’t yet been able to fix a date,” the BBC said. The Conservatives also said “discussions are ongoing”.

BBC sources insisted that they remained optimistic the prime minister will not be tempted to duck the challenge.

One senior Conservative source expressed surprise that Labour appeared to have been told all the party leaders had signed up to be interviewed by Neil, insisting no final decision had yet been made about Johnson’s participation.

The prime minister has agreed to other broadcast events during the campaign, including last Friday’s Question Time special, and the Tories believe that will insulate him from the charge of cowardice even if they decide to skip the Neil interview.

Corbyn’s interview with the broadcaster resulted in widespread negative press coverage, after the Labour leader did not apologise directly over antisemitism within the Labour party and was grilled over his funding of a £58bn boost for women caught out by changes to the state pension age.

All the other major party leaders have agreed to take part in the one-on-one interviews with Neil. Jo Swinson will appear next Wednesday and the Brexit party leader, Nigel Farage, will take part on Thursday. This leaves just three potential slots for the prime minister.

The chair of the Labour party, Ian Lavery, said on Wednesday: “Boris Johnson backed out of a head-to-head debate with Jeremy Corbyn on Sunday, he is refusing to take part in the party leaders’ climate crisis debate tomorrow and now this.

“He’s running scared because every time he is confronted with the impact of nine years of austerity, the cost of living crisis and over his plans to sell out our NHS, the more he is exposed.”

Political parties are increasingly confident in their ability to ignore certain channels and dictate the terms of engagement for debate appearances, amid falling broadcast news figures. Channel 4 cancelled its head-to-head leadership debate planned for last weekend after Johnson refused to take part, while Sky News has been completely left out of the televised debates this election.

Both Labour and the Conservatives have agreed debate formats with broadcasters which ensure their leaders cannot be challenged directly by smaller parties, despite legal action from the Lib Dems and the SNP.

The BBC will show a seven-way leadership debate between all the major parties on Friday night but both the Conservatives and Labour have declined to send their leaders. Instead, Rishi Sunak will deputise for the Tories and Rebecca Long-Bailey will stand in for Labour.

Channel 4 is due to show a climate-focused debate on Thursday featuring Corbyn, the SNP leader, Nicola Sturgeon, the Lib Dem leader, Jo Swinson, and the Green co-leader Siân Berry. The Conservatives have offered to send Michael Gove in place of Boris Johnson to avoid the prime minister being empty-chaired, while the Brexit party is boycotting it, as it has “no faith that the broadcaster will conduct this debate in a fair and objective way” due to its “remain position”.