Mr Farage said the Remain campaign were “scared witless” about the prospect of defeat on June 23 and were trying to create a link in voters’ minds between her killing and the EU vote.
He also dismissed the defection to the Remain camp of former Conservative chair Sayeeda Warsi as a “Number 10 put-up job”.
Ms Warsi said her decision to change sides was sparked by a “xenophobic” poster released by Mr Farage, and “lies” from Michael Gove over the prospect of Turkey joining the EU. But her announcement was greeted with bemusement by Leave campaigners, who said they were not aware the Muslim peer had ever been a Brexit supporter.
Mr Cameron has faced criticism from for retweeting a link to the last article written by the Batley & Spen MP, in which she argued Britain could deal with immigration more effectively by remaining in the EU.
Mr Farage, who acknowledged on Sunday Ms Cox’s death had taken momentum out of the Leave campaign, told LBC radio: “I think there are Remain camp supporters out there who are using this to try to give the impression that this isolated horrific incident is somehow linked to arguments that have been made by myself or Michael Gove or anybody else in this campaign, and frankly that is wrong.”
He insisted he had said nothing “inciteful” during the campaign, adding: “What we are seeing here is the prime minister and the Remain campaign trying to conflate the actions of one crazed individual with the motives of half of Britain who think we should get back control of our borders and do it sensibly...
“We have a prime minister and a chancellor and other big political leaders in Britain who are scared witless.
“They thought they would win this referendum by a country mile. They know it’s neck and neck, they know it’s down to who turns out on the day to vote, and there is no level of denigration or false association that they will not stoop to, but I think people are intelligent enough to see through this sort of thing.”
Asked whether he was using the MP’s death for political advantage, Mr Cameron said: “What I have been talking about in respect of Jo is what a wonderful human being and great politician and great campaigner she was.”
He added: “Last week a brilliant member of parliament, a loving mother, a loving wife was tragically murdered on our streets.
“What everyone has been saying, and what I say again, is paying tribute not only to her but the values she lived by and epitomised in public life of tolerance, of service, of community. That’s what we are saying about her.”
Mr Cameron said there were “good ways” of controlling immigration through changes to the welfare system, but added: “A bad thing to do would be to leave the single market, costing jobs, hurting businesses and hurting families’ finances right up and down the country.”