In an interview with The Times Mr Cameron, who is promoting his upcoming memoirs, accused Boris Johnson and Michael Gove of “trashing the Government” during the 2016 EU referendum debate. He also suggested another EU membership referendum might be needed to “unblock” parliament.
She commented: “We’ve seen what happens when ex prime ministers come back onto the scene with Tony Blair, with John Major, it’s never good news for Brexiteers.
“He’s just here to frustrate the situation even further.”
Ms Harris founded the pro-Brexit group Leavers of London, as a space for Brexiteers in the capital to get together and socialise.
The group has since changed its name to Leavers of Britain, and launched nationwide.
Mr Cameron was fiercely critical of Mr Johnson and Mr Gove, and claimed their assertion during the 2016 referendum that Turkey could join the EU was “ridiculous”.
Discussing the referendum campaign he said: “I loved the explaining and arguing and that side of politics, persuasion, but then, as it went on, I just felt more and more bogged down.
“It turned into this terrible Tory psychodrama and I couldn’t seem to get through.
“What Boris and Michael Gove were doing was more exciting than the issues I was trying to get across. I felt like I was in a sort of quagmire by the end.”
Mr Cameron also suggested his former colleagues hadn’t reflected their true views during the referendum campaign.
Both Mr Johnson and Mr Gove backed the official pro-Brexit ‘Vote Leave’ campaign.
The former Prime Minister asserted: “Boris had never argued for leaving the EU, right?
“Michael was a very strong Eurosceptic, but someone whom I’d known as this liberal, compassionate, rational Conservative ended up making arguments about Turkey joining and being swamped.
“They were trashing the government of which they were a part, effectively.”
Mr Cameron announced his resignation as Prime Minister on 24 June 2016 immediately after the Brexit result was confirmed.
He called the referendum after UKIP made an electoral breakthrough and picked up two former Tory MPs via defections.
In the interview Mr Cameron admitted he is worried about Britain’s future.
He asserted: “Every single day I think about it, the referendum and the fact that we lost and the consequences and the things that could have been done differently, and I worry desperately about what is going to happen next.
“I think we can get to a situation where we leave but we are friends, neighbours and partners.
“We can get there, but I would love to fast-forward to that moment because it’s a painful memory for the country and it’s painful to watch.”
Current Prime Minister Mr Johnson had vowed to take Britain out of the EU on October 31 with or without a formal exit deal.
However Parliament has since passed a vote making a no deal Brexit illegal without its explicit consent.