Liberal Democrat leader Jo Swinson should be allowed to take part in TV election debates as a way of “inspiring girls and women into leadership roles”, the party’s female MPs, MEPs and peers have demanded.

The group issued the plea in an open letter to broadcasters, following ITV’s announcement that Swinson would be excluded from the first debate between Boris Johnson and Jeremy Corbyn on 19 November.

Nine female Lib Dem MPs wrote to broadcasters demanding that the only woman leading a UK-wide party be included as a way of combating the intimidation that female MPs face. “As Liberal Democrat women, we are immensely proud to have elected our first woman leader,” they wrote. “We believe it is important, in terms of inspiring girls and women into leadership roles in future, that the only woman to lead a major UK party is not locked out of the leadership debates.

“Over the course of this parliament, women in particular have been subjected to verbal abuse and threats of violence, with many deciding not to seek re-election. We have also seen, in our wider society, outrage at the discrepancies between the pay of men and women in some of our greatest institutions... Sadly, these issues of discrimination and marginalisation of women still remain relevant, and must be challenged.”

The lack of official rules concerning TV debates means the process is a complicated negotiation between parties and broadcasters.

The November debate would be the first direct confrontation between the Tory and Labour leaders since TV debates began in 2010. That election saw three three-way debates between David Cameron, Gordon Brown and Nick Clegg, and resulted in an outbreak of “Cleggmania” as the Lib Dem leader was credited with winning many of the exchanges. While the Lib Dems ended up with fewer seats, insiders say the debates allowed the party’s polling to recover, compared with the start of the campaign, and helped it to a record number of votes.

The Lib Dems are angry that Swinson is not being allowed that chance. “Jo is our candidate to be prime minister, and has the right to debate the other major party candidates,” writes the group of female politicians. “For the last six months, the party has been gaining momentum in the polls, and are now consistently polling at or around 20%, and we beat both Labour and the Conservatives in the last national elections in May.

“If Jo were not to be included in the leadership debates that are proposed, it would deny these people a voice. Her exclusion would fail to represent any balance or provide a platform for a unique position that has undeniably garnered significant public support.”

The frontrunner usually avoids the debates as they can derail campaigns, but Johnson’s team have been keen to put the prime minister up against Corbyn, with polls suggesting that the public see him as more prime ministerial. Labour, however, back Corbyn to win the support of viewers with his plans to reduce poverty.

Downing Street sources have indicated that any debate involving smaller parties may be avoided by Johnson, who could send a cabinet minister in his place. However, when Theresa May made a similar decision in 2017, it was regarded as a of the mistake in an error-strewn campaign. Johnson ignored a head-to-head debate with Jeremy Hunt during the Tory leadership election, but took part in a chaotic debate that included five contenders.