The TV broadcaster is planning a live head-to-head TV showdown between Conservative leader Boris Johnson and his Labour counterpart Jeremy Corbyn, with other political leaders left out of the debate format.
Both the Lib Dems and the Scottish National Party have challenged this stance, arguing their exclusion is “undemocratic” and a breach of the usual rules of election fairness.
Launching the judicial review on Monday morning, Guy Vassall-Adams QC, for the Lib Dems, told the High Court: “The voice of Remain has been excluded – the Lib Dems are the most plausible candidate to be the voice of Remain.”
In a written statement, he said: “The decision by ITV to not include the Liberal Democrats in the debate breaches the duty of due impartiality and the requirement that ITV must include, and give due weight to, an appropriately wide range of issues of major political controversy.
“The dominant issue of this election campaign is Brexit, which is on any view a matter of major political controversy and current public policy.
“In the first national TV debate of the campaign, it is essential that a wide, balanced range of views on Brexit is represented.
“But the only invitees are supporters of Leave, with the Conservative advocating Leave and Labour proposing to negotiate its own deal to Leave.
“The views of millions of Remain-supporting voters, regardless of party affiliation, will not be represented in this debate.
“This has serious consequences for the fairness of the democratic process of which leaders’ debates, a form of hustings, form a significant part.”
The Lib Dems say ITV’s proposal to follow the debate with interviews with other party does not make up for missing out on the main event.
“The debate itself will be watched by many millions of people who want to see the party leaders interacting with each other on the major issues of the campaign including Brexit”, said Mr Vassall-Adams.
He added that former Lib Dem leader Nick Clegg was included in a 2010 debate when the party was polling at similar levels to now.
The party says it is not seeking a court order that it should be included in the debate or the programme be cancelled, but says it wants ITV’s decision to be declared unlawful and leave it to the broadcaster to decide what to do next.
The SNP is also arguing that ITV is breaching impartiality rules by excluding its leader Ian Blackford from the debate, depriving Scottish viewers of a major party in its electoral system.
Lib Dem party president Sal Brinton has said it is “vital for our democracy to have both sides of the Brexit debate represented at the top table of the leaders' debates."
ITV is fighting the judicial review, arguing it has met impartiality regulations of OfCom with the format proposed and is planning another multi-party debate ahead of the December 12 General Election.
Sky News is also proposed a November 28 date for its debate, while the BBC has confirmed it will host two debates, on November 29 and December 6, in addition to a series of Question Time specials.
The hearing before Lord Justice Davis and Mr Justice Warby continues.