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The head of Channel 4 News has branded Boris Johnson a "known liar" and compared the Prime Minister to Russia's Vladimir Putin.

Dorothy Byrne said broadcasters should be more direct in calling out deliberate untruths by Britain's politicians in a hard-hitting lecture last night.

She compared the Tory leader to Vladimir Putin as she outlined his preference for recording a "jolly statement" over a grilling on television.

Ms Byrne told the annual MacTaggart Lecture at the Edinburgh TV Festival: "What we all need to decide: what do we do when a known liar becomes our Prime Minister?

"I've talked to journalists from several television organisations about this issue.

"They said they would be loath to use that word 'liar'.

(Image: PA)

(Image: Getty)

"Remember when Andrew Marr told Penny Mordaunt her claim that the UK couldn't stop Turkey from joining the EU was 'strange'?

"It was strange, but it was also untrue - a lie.

"Is it time for us to start using the L-word? I believe that we need to start calling politicians out as liars when they lie.

"If we continue to be so polite, how will our viewers know that politicians are lying?"

Boris Johnson has repeatedly lied over his three-decade rise to power.

The Times sacked him in 1988 for making up a quote in a front-page story.

(Image: Getty)

In 2004 he was sacked as Tory vice chair and Shadow Arts Minister after aides to leader Michael Howard decided he had lied about an affair.

And in 2016 he was a figurehead of the Vote Leave campaign, spreading their lie that the UK sent the EU £350million a week even after it was condemned by the UK Statistics Authority.

Ms Byrne did not only have Boris Johnson in her sights in the searing lecture.

She said both the Prime Minister and Jeremy Corbyn are "cowards" who refuse to hold themselves up to proper scrutiny on television.

The journalist, who is among the longest-serving heads of news and current affairs in British TV, said: "I would never have thought I would say these words.

"I believe that Mrs Thatcher would agree with me. Boris Johnson and Jeremy Corbyn are cowards. She had a word for men like them - 'frit'.

(Image: PA)

"If they really believe in the policies they promote, they should come onto television to explain them, to allow them to be scrutinised and to justify them.

"And just this weekend we read that these cowardy-cats in the Tory party may stop junior ministers from going onto the Today programme.

"I have previously described listening to Today as like accidentally walking into a knitting shop in Bournemouth.

"But even I accept that millions listen to it and they have a right to hear from their political leaders on it."

Ms Byrne said the decrease in politicians holding themselves up to scrutiny on TV has become "critical for our democracy".

She added: "We have a new Prime Minister who hasn't held one major press conference or given one major television interview since he came to power.

(Image: PA)

"That cannot be right. And we have a leader of the Opposition who similarly fails to give significant interviews on terrestrial TV. We may be heading for an election very soon.

"What are they going to do then? I genuinely fear that in the next election campaign there will be too little proper democratic debate and scrutiny to enable voters to make informed decisions."

She also blasted former prime minister Theresa May , saying: "Throughout her time as PM, May's longest interview with Channel 4 News was seven minutes.

"How do you delve into the complex problems of our times in a few minutes? Jeremy Corbyn sometimes permits only one question, and then doesn't answer it."

A Labour Party spokesperson later said: "In a standard week, Jeremy Corbyn is interviewed by a wide range of journalists and regularly gives longer in-depth interviews."