In response, GB News chief executive Angelos Frangopoulos said the fine was a “direct attack on free speech and journalism in the United Kingdom”.
“We believe these sanctions are unnecessary, unfair and unlawful,” he added.
The hour-long show, which aired on 12 February, saw members of the public put questions to the then-prime minister.
However, Ofcom received 547 complaints about the programme.
The regulator found earlier this year that while featuring Mr Sunak was fine in principle, “due weight” should have been given to an “appropriately wide range of significant views” other than the Conservatives.
It said the then-prime minister “had a mostly uncontested platform to promote the policies and performance of his Government in a period preceding a UK General Election,” which it recorded as a breach of impartiality rules.
On Thursday, Ofcom said “given the seriousness and repeated nature of this breach,” it has imposed a £100,000 financial penalty on GB News.
Mr Frangopoulos said in response that the programme “was an important piece of public interest programming” and that “appropriate steps” were taken to ensure due impartiality.
He added: “It was designed to allow members of the public to put their own questions directly to leading politicians.
“GB News chooses to be regulated and we understand our obligations under the Code.
“But, equally, Ofcom is obliged by law to uphold freedom of expression and apply its rules fairly and lawfully.”
A man who died after being hit by a bus in Edinburgh has been named.
Michael Leneghen, 74, died after being struck at around 7.25pm on Saturday 2 November in the Cowgate area of the city.
On the day of the incident, police issued a warning for members of the public not to share distressing images and videos circulating online.
In a statement, Mr Leneghen’s family thanked members of the public and emergency services who were involved and asked for privacy.
A single-decker bus collided with Mr Leneghen, who was on foot, Police Scotland say.
Sergeant Paul Ewing of Edinburgh‘s road policing unit said the force’s thoughts were with Mr Leneghen’s family and friends “as well as everyone affected by this tragic incident”.
“Our enquiries remain ongoing. We have already spoken to a number of people who were in the area at the time and work is ongoing to check public and private CCTV footage,” he added.
“We are still keen to hear from anyone who has not yet spoken to police.”
Chief Inspector Trisha Clark, the local area commander, previously said police were “aware of videos and images circulating on social media which are causing distress to the deceased’s family”.
“We would ask members of the public not to share them out of respect for his family, and to report them to the relevant social media platform to prevent further circulation,” she added.
MP Mike Amesbury has been charged with common assault following an incident in Frodsham, Cheshire, last month.
The charge comes after a video emerged of him appearing to punch a man to the ground.
Cheshire Police said the 55-year-old will appear at a magistrates court at a later date to face the assault charge.
In a statement, police said the charge “relates to reports of an assault on a 45-year-old man on Main Street, Frodsham, which was reported to police at 2.48am on Saturday 26 October”.
Rosemary Ainslie, head of the Crown Prosecution Service’s special crime division, said: “Following a review of the evidence provided by Cheshire Police, we have authorised a charge of common assault against Mike Amesbury MP, 55.
“The charge follows an alleged assault in Frodsham, Cheshire, on Saturday, 26 October 2024.
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“The Crown Prosecution Service reminds all concerned that criminal proceedings against the defendant are active and that he has the right to a fair trial.”
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In a statement, Mr Amesbury said: “I have today been summonsed to court to face a charge of common assault following an incident in Frodsham last month, which was deeply regrettable.
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“I am continuing to cooperate with police and given this is an ongoing case I cannot comment further.”
Labour suspended Mr Amesbury from the party so he is now an independent MP for Runcorn and Helsby.
A reportedly well-known Premier League figure is the subject of a Football Association (FA) safeguarding inquiry.
It follows allegations of sexual offences perpetrated by the man – cases which have since been dropped by police.
A spokesperson for the FA said: “We have robust safeguarding measures in place, and all referrals into us are handled in line with our policies and procedures.
“We investigate and assess all allegations and concerns about individuals who may pose a risk of harm to children and adults at risk in football and, where applicable, can impose proportionate safeguarding measures in accordance with FA safeguarding regulations.