Nigel Farage has boldly claimed that the SNP are "openly racist" towards English people and described their behaviour as "totally extraordinary".
The Ukip leader made the comments during a speech to party supporters in Hartlepool, where he claimed the local fishing industry had been destroyed by European Union (EU) regulations.
''The biggest racism I have seen in British politics is happening north of the border where some of the anti-English hatred is reaching a truly astonishing level," he said.
"The SNP are openly racist. The anti-English hostility and the kind of language that is used about and towards English people is totally extraordinary."
Farage added: "If my supporters behaved in the way that some of those pro-independence supporters behaved in the referendum I'd have been painted out to be the worst person that had been seen for 70 years in British politics."
The MEP and South Thanet candidate also stressed that Ukip, which has been caught up in a number of racism rows in the run-up to the election, is a "non-racist, non-sectarian" party.
But the SNP did not take the allegations of racism lightly and subsequently hit back at Farage's "disgraceful" remarks.
"These disgraceful comments – which aren't just offensive to the SNP, but to the majority of people in Scotland on current polls - show exactly why the people of Scotland reject Ukip," said Humza Yousaf, an MSP for the SNP.
"Farage's politics of fear and intolerance have been exposed in this campaign, and he has still not apologised for David Coburn MEP comparing me to a convicted terrorist merely because I am a Muslim.
"The SNP have been clear that we will be a positive voice for people across the UK – and with progressive policies such as ending austerity to invest in public services and our NHS, we can bring real change north and south of the border. All Ukip have to offer is nasty rhetoric."