The veteran broadcaster told the Daily Mail he warned the board time again that the station was not ready to launch and said one of the technical problems faced in the early days was the channel “couldn’t light people of colour”.
Neil announced his departure from the fledgling channel in a tweet earlier this month where he said it was “time to reduce my commitments on a number of fronts”.
But the split between the new channel and its chairman and lead presenter has become increasingly bitter, with the 72-year-old since saying he “couldn’t be happier” to have severed ties.
In his Daily Mail interview, Neil said he walked away from a £40m contract – but that continuing with the channel “would have killed me”.
Speaking about the technology issues faced by the channel, he told the newspaper: “That stress was just huge. It meant you couldn’t think about the journalism.
“You were just constantly wondering: ‘Will we make it through the hour?’”
Neil said at one point, the “whole system went down” and had to be rebooted, with the channel going on air with 15 seconds to spare.
“By the end of that first week, I knew I had to get out. It was really beginning to affect my health. I wasn’t sleeping. I was waking up at two or three in the morning,” Neil said.
“I had a constant knot in my stomach. When I did wake up I’d feel fine, then remember all the problems I had with GB News and this knot would come and wouldn’t leave me for the whole day.”
He also said the studio had issues with lighting, including in the area where he did his show from, which he said was “so black I had to take my jacket off and wear a white shirt”.
“We were also broadcasting from the most diverse, multi-ethnic city in the world and we couldn’t light people of colour. In the early days you could barely see them for our backdrop,” he added.
“They faded into the background because we didn’t light them properly.”
Neil claimed he warned executives that the channel – which was hit with a host of technical issues after it launched – was not ready before it went on air.
“At Sky, we’d had three weeks of rehearsals before going on air. GB News barely had a week and there were so many hitches with the technology,” he said.
Last week, the 72-year-old resigned as the chair of GB News and announced he would be stepping down as lead presenter three months after leading its launch.
During an appearance on the BBC’s Question Time, Neil said the direction the channel had taken was not the same one envisaged beforehand and he resigned because he did not want to be a part of a “British Fox News”.
The 72-year-old told the Daily Mail: “I’m angry that what should have been my last big media gig – which, if we’d made it work, could have been great – turned out to be the worst eight months of my career, the worst by far, from early January to last week.”
In a statement from the channel carried by the Mail, a GB News spokesperson said: “At no point did Andrew raise concerns of the editorial direction of GB News moving to the right.
“As with all companies, decision-making rests with the board, and GB News is no different. As a member of the board, Andrew had the same rights and abilities to raise concerns, and he was privy to all decisions.”
They added: “The board allowed Andrew time off over the summer to recharge his batteries. He subsequently asked to leave and the board agreed to this request. The terms of his departure were properly negotiated and documented, with Andrew taking legal advice throughout.”
Additional reporting by Press Association