Nigel Farage has accused the BBC of "bias" in its coverage of UKIP's election campaign.
The UKIP leader said the BBC was part of the "political establishment" which covered the election "as if there were just two choices in England".
The comment to reporters came ahead of a BBC Question Time leaders' debate featuring David Cameron, Ed Miliband and Nick Clegg.
Mr Farage will answer questions in a separate programme later.
There will be versions with the SNP's Nicola Sturgeon and Plaid Cymru's Leanne Wood in Scotland and Wales.
In Northern Ireland, there was a leaders debate on 16 April as part of the BBC Newsnight programme, with Nigel Dodds of the DUP, Sinn Fein's Mairtin O Muilleoir, Ulster Unionist leader Mike Nesbitt, the SDLP's Mark Durkan, and Alliance leader David Ford.
"There was the Ofcom ruling that said there were four major parties [in England]," Mr Farage told reporters during a campaign walkabout in Aylesbury.
"I've got no complaints about Channel 4, ITV, Channel 5, Sky, who have covered us as part of the election campaign. You know, the good bits, the bad bits and all the things that happen.
"But I genuinely feel that if you were to watch the evening news on the BBC you would think that UKIP were just a bit part player."
Major party status
He added: "We have this bizarre state of affairs where the BBC, an organisation we are all charged £145 a year to have the benefit of seeing, aren't regulated by Ofcom, have made their own minds up (about major party status) and frankly produce the News at 10 every night as if there were just two choices in England in this election.
"I think they are biased, I thought last night's report they produced on the South Thanet constituency was frankly outrageous."
Later he told BBC political correspondent Robin Brant: "It is as if the BBC is part, in its thinking, of the political establishment and we are the one party in British politics challenging this European consensus and frankly I think being treated in the most extraordinary way.
"When we have people in UKIP that say or do stupid things, and it happens, I have to hold my hands up and the BBC covers it as a news story."
During a BBC debate with opposition party leaders on 16 April, the UKIP leader accused those attending of being a "left-wing audience".
However, he said he would take part in the latest BBC debate.
"We will see what we get tonight with the audience.
"What I do know is the real audience will be sitting at home and I will do my best, albeit rather late having been excluded from the main debate, to do what I have tried to do through this whole general election campaign.
"That is to tell the truth, even if at times the truth is difficult to hear."
UKIP has also complained to the police over comments about Mr Farage on an episode of BBC One's topical quiz Have I Got News For You.
The BBC said the show often made jokes at the expense of politicians. Kent Police said it would not take action.
A full list of candidates standing in Thanet South is available here.