A leading advocate for Britain leaving the EU has condemned the use of personal attacks on David Cameron by the Brexit camp saying it has been a "mistake" to question the PM's integrity.
Frank Field, a former Labour minister, 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."
It came as Cameron came under fire from Conservative colleagues with senior Vote Leave campaigners branding him "corrosive".
Conservatives Leave campaigners have been lining up to criticise Prime Minister David Cameron this weekend over immigration and his views on Britain remaining in the EU.
Labour's Alan Johnson, campaigning for the Remain camp, called the Conservative infighting "very ugly".
ITV News political correspondent Lewis Vaughn Jones reports.
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Conservative MP and Leave campaigner Nadine Dorries has said Prime Minister David Cameron will be "toast within days", depending on the result of the European referendum.
Speaking to Robert Peston on ITV's Peston on Sunday, she said her "letter is already in", along with 50 other MPs, asking for the Prime Minster to stand aside.
She said "David Cameron might just survive if there's a 60/40 majority to Remain" but warns anything less should see the end of his leadership.
"He has lied, profoundly. There are many issues at which David Cameron has told outright lies and the trust, because of that, has gone from both him and George Osborne", Dorries said.
She added: "I always have backed the only politician in Westminster who has a proven track record of achievement, and that's Boris Johnson".
Newly elected London mayor Sadiq Khan has criticised both EU Leave and Remain campaigns for "talking nonsense".
Speaking to Robert Peston on ITV's Peston on Sunday, Mr Khan said the public should hear a "positive and patriotic case" instead of "too much project fear".
He said: "One side is saying if we remain in the European Union, it's the end of time. The other side is saying if we leave the European Union it's the end of the world as you know it".
Khan added there's a "patriotic case for our city's interest to remain in the EU" and said London has always been "open-minded, outward-looking [and] embracing cultures".
Meanwhile the London mayor has defended criticism after agreeing to spend Monday on the Remain campaign trail alongside Prime Minister David Cameron - apparently against the wishes of Labour leader Jeremy Corbyn.
"We're never going to be best friends... I'm willing for us to put aside our differences, put aside the grudges that he or I may have, but this debate is far more important than David Cameron or me", he added.
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Brexit campaigner Dr Liam Fox has said that if Britain votes to leave the European Union "the best thing" would be for David Cameron to stay on as prime minister.
Speaking to the BBC's Andrew Marr show, the former defence secretary said: "We will need to have a government position before we enter into negotiations under article 50.
"We need a period of stability and whatever our views have been during the referendum, we need to put to bed all those personal views and understand that stability for the country is the most important element."
It comes as Conservative MP Andrew Bridgen criticised Mr Cameron, insisting he is "finished" as Tory leader because of the way his "Operation Fear" tactics have divided the party.
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