The Brexit camp's highly personalised onslaught on Prime Minister David Cameron has been condemned by a leading Out advocate.
Labour former minister Frank Field warned that "putting sticky fingers into people's souls" would backfire for the Leave push.
The interventions followed a weekend of Tory warfare in which pro-Brexit Conservative MPs branded Mr Cameron "corrosive" and a "liar" as they openly plotted to try to oust him even if Remain achieves a narrow win in the referendum.
Mr Field told BBC Radio Four's Westminster Hour. "The first mistake I think our side has made has been to question the Prime Minister's integrity. I think it's a mistake to put your sticky fingers into people's souls and say they're debasing public life.
"I think it would be very good for our Out campaign to actually concentrate on issues and not on the integrity of the other side."
Tory Lord Finkelstein said that while rebel claims they could muster the 50 signatures needed to force a no confidence vote in the Prime Minister were probably true, it would be much harder to bring him down.
"I think it will not be difficult to find 50 people who are discontented with David Cameron at the end, probably more, but I think it would be very hard to produce a majority of the Conservative Party that wanted to remove him.
"And that I think will make even those who are against him think twice before they start a letter campaign that might end up strengthening him not weakening him," he told the BBC.
The comments came after arch backbench critic Nadine Dorries predicted Mr Cameron would be "toast" even if Remain edged a win in the June 23 referendum.
The Mid-Bedfordshire MP said she had already sent a letter to the 1922 backbench committee, which she indicated called for a no confidence vote in Mr Cameron.
"If the Remain campaign wins by a large majority, I'd say it would have to be 60-40, then David Cameron might just survive, but if Remain win by a narrow majority, or if Leave, as I certainly hope, will win, he's toast within days. There are many issues about which David Cameron has told outright lies," Ms Dorries told ITV.
Fellow Brexiteer MP Andrew Bridgen insisted more than the 50 colleagues needed to trigger such a poll were ready to move against the Prime Minister, as Boris Johnson branded Mr Cameron "corrosive".
The PM was campaigning alongside London mayor Sadiq Khan in a show of cross-party unity even though Mr Cameron lambasted the Labour figure's "poor judgement" just weeks ago during the bruising battle for City Hall.
Mr Khan defended his decision to share a platform with Mr Cameron - despite Labour MPs shouting the Prime Minister down in the Commons as a "racist" when he attacked the now mayor - because he said Remain was in London's interest and he did not want to hold grudges.
Mr Cameron was set to try to brush off the Tory squall over his future as he attempts to shift the battle back on to the economic impact of Brexit.
Number 10 dismissed the personal attacks as a "distraction" intended to move attention away from the economic arguments for Remaining in the EU.
Meanwhile, green belt land will have to be sacrificed to housing estates in order to deal with continued mass migration, pro-Brexit Cabinet Minister Chris Grayling warned.
Pressure on public services, and the move to build on previously protected countryside, will be the price of staying in the EU, according to the Commons Leader.
Mr Grayling warned that migration from the rest of the EU will "change the face" of the UK forever, according to the Daily Telegraph.
And the Remain campaign accused Mr Johnson of being unable to give clear answers when asked the future of British farming, and the level of agricultural subsidies post-Brexit on BBC's Countryfile.