The Lib Dems and SNP have lost their legal challenge to be included in an ITV head-to-head debate ahead of the general election on 12 December.
The channel is due to air a face-off between Tory leader Boris Johnson and Labour's Jeremy Corbyn on Tuesday.
The Lib Dems said they wanted their pro-Remain stance to be represented, while the SNP also wanted the issue of Scottish independence to be raised.
In the High Court in London, Lord Justice Davis and Mr Justice Warby said the case was not suitable for judicial review as ITV was not carrying out a "public function" in law by holding the debate.
However, the parties had the right to complain to Ofcom about the programme after it had been broadcast, they said.
Lord Justice Davis said: "The clear conclusion of both members of this court is that, viewed overall, these claims are not realistically arguable."
But Lib Dem education spokeswoman Layla Moran tweeted "the fight must continue", adding: "It is outrageous that the Remain voice is missing from the ITV debate.
"It's simply wrong of broadcasters to present a binary choice and pre-empt the decision of the people in a general election."
The SNP's Westminster leader, Ian Blackford, also condemned the decision, saying it "discriminated against Scottish voters" and "treated them as second-class citizens".
He added: "That is, quite simply, a democratic disgrace, and the fact that election law and broadcasting codes allow such gross unfairness is unacceptable."
And he called for Mr Johnson and Mr Corbyn to commit to take part in an all-party debate on 1 December, rather than sending other senior figures from their respective parties.
A case of editorial judgement
Analysis by Tom Symonds, BBC home affairs correspondent
It took the two judges just a matter of 10 or 15 minutes to reach a decision about the claim that the Lib Dems and SNP should be allowed access to the head-to-head debate.
The judges came back and said they would not agree to that and effectively refused to even hear the judicial review.
Their legal argument was that ITV was not exercising a public function as it is a private broadcaster - albeit regulated - therefore could not be subject to judicial review.
They also said if the two parties had a complaint about the programme, they had a way of complaining and that was to the regulator Ofcom - but that can only be done after the programme is broadcast
However, the judges said an important part of their decision was the editorial judgment made by ITV was not irrational and perverse.
They did not want as judges to get in the way of an editorial matter for a major broadcaster.
So the application from the parties is rejected and the debate goes ahead.
But the Lib Dems still have big problems with this court decision, and say they they are going to take a closer look before deciding what to do next.
The BBC will also host a live head-to-head debate between the Conservative and Labour leaders in Southampton on 6 December, plus a seven-way podium debate between senior figures from the UK's major political parties on 29 November, live from Cardiff.
The Lib Dems have sent a legal letter to the BBC over its decision not to include Ms Swinson in the head-to-head.
BBC Scotland will stage a televised debate between the SNP, Conservatives, Labour and Liberal Democrats on 10 December, although the Scottish Greens have criticised the decision not to include them.