Boris Johnson has said he “regrets” describing long Covid as “bollocks”.
But charities representing people with the condition said the former prime minister “only apologised because he got found out”.
The UK Covid-19 Inquiry heard that Mr Johnson made a number of “disparaging” remarks about the condition during his time in office.
A document from October 2020 described symptoms of the condition, beside which he wrote “bollocks” and “this is Gulf War Syndrome”.
Counsel to the inquiry, Hugo Keith KC, said: “You were I think less sympathetic to the needs of those persons suffering from long-term sequela, that is to say, suffering from the condition (known) as long Covid.
“You questioned for quite some time whether or not that condition truly existed and you equated it to Gulf War syndrome repeatedly, is that fair?”
Mr Johnson replied: “Not really, no.
“The words that I scribbled in the margins of submissions about long Covid have obviously been now publicised and I’m sure that they have caused hurt and offence to the huge numbers of people who do indeed suffer from that syndrome.
“And I regret very much using that language and I should have thought about the possibility of future publication.”
He said he was trying to “get to the truth of the matter” of what the syndrome was.
Mr Johnson told the inquiry that he only got a “proper” paper on long Covid in the summer of 2021.
Mr Keith told the inquiry that Mr Johnson “continued to make disparaging references to whether or not this is Gulf War syndrome stuff” in February 2021, and again in June 2021.
The inquiry has also previously been shown a WhatsApp message from February 2021, where Mr Johnson said: “Do we really believe in long Covid? Why can’t we hedge it more? I bet it’s complete Gulf War Syndrome stuff.”
Mr Johnson told the hearing: “It’s no disrespect to long Covid patients and I saw in the victim impact videos are some of the victims of long Covid, I can imagine what a dreadful thing is.
“But there are also, with Gulf War syndrome, many people who have terrible symptoms for a very long time.
“There are also people who think they may be suffering, I think this is the now accepted, from something associated with the Gulf War, but who are not in fact suffering from something associated with the Gulf War.
“So what I was trying to say was ‘where is the, where is the line’? And ‘please can someone explain to me what this is?’
“Because I was getting anecdotal accounts of people who were suffering from it, and I wanted to be able to say what we understood it to be and what we were doing about it.
“And what we were doing about it is fighting Covid, because the way to stop long Covid is to, is to stop Covid.”
Commenting on the remarks, Sammie McFarland, chief executive of Long Covid Kids, said: “Boris Johnson didn’t apologise for using the language because it was wrong; he only apologised because he got found out and his actions have caused years of bullying and stigma for people suffering from Long Covid.
“We need a sincere apology.
“But more than that we need action and the inquiry to create meaningful and impactful recommendations going forward.
“Johnson also said that people think they are unwell. He needs to recognise that this is a real disease and a consequence of the pandemic alongside the unfortunate deaths and hospitalisations.”