Simon Clarke, a Conservative MP, hit back immediately, saying: “That’s an extraordinary thing to say. Are you impugning the prime minister’s integrity?
“It is genuinely wrong to question how sick the prime minister was, he was in intensive care and very, very ill. We shouldn’t allow that to pass without comment.”
Ms Vaz did not withdraw the claim, on the BBC’s Politics Live programme, but backtracked partially by admitting: “Honestly I don’t know – I’m not his doctor.”
Mr Johnson spent three nights in intensive care, in London’s St Thomas’ Hospital, because of “persistent” coronavirus symptoms.
Dominic Raab, the foreign secretary, was put in charge of running the government and the prime minister was out of action recovering for several weeks afterwards.
He was given oxygen, but was not placed on a ventilator, and is believed to have remained conscious throughout his ordeal.
After leaving hospital, Mr Johnson posted a five-minute video message on Twitter in which he said “the NHS has saved my life, no question”.
He named and thanked nurses who had cared for him, having stood by his bedside for 48 hours “when things could have gone either way”.
“The reason, in the end, my body did start to get enough oxygen was because for every second of the night they were watching and they were thinking and they were caring and making the interventions I needed,” the prime minister said.
And his fiancée, Carrie Symonds, said: “There were times last week that were very dark indeed. Today I’m feeling incredibly lucky.”
Put under pressure over her allegation, Ms Vaz attempted to deflect the focus of the discussion onto Dominic Cummings, the ousted former chief aide now locked into a bitter war of words with Mr Johnson.
“People have died. We’re talking about Dominic Cummings giving evidence [on Wednesday], aren’t we,” she said.
“The issue is he was there. he will have made judgement calls with or without the prime minister at the time.
“He was the right hand of the prime minister, making important decisions. There are 27,000 people who have died.”
In a statement later, Ms Vaz said: “I wish to clarify my remarks and apologise if any offence was caused. I never intended to give the suggestion that the prime minister was not seriously ill.”