Yvette Cooper has accused the Leave campaign of being 'un-British' by "pitting human beings against other human beings".
The Labour MP and former shadow home secretary was speaking out during a debate on Britain's membership of the EU just hours before the polls opened.
Cooper attacked leading Brexit campaigners and claimed they had "pushed lies" on the public.
She also took aim at a poster launched by Ukip earlier this week, which was branded "vile" and "racist" by Nicola Sturgeon at the time.
Cooper claimed the referendum "has become about what it means to be British", commenting that "being British is not being the kind of country we have seen in Nigel Farage’s posters".
She continued: "We have seen an increase in the last few months in the level of vitriol...
"If you’re not going to be honest about things, if you’re not going to be straight with people, if you’re going to try and pitch communities against each other, than that escalates tension."
Her comments were echoed by the official StrongerIn campaign, who accused Farage of peddling "dog-whistle politics".
In the same Channel 4 debate, Cooper was challenged by an audience member who claimed they were often made to "feel racist or xenophobic when you bring these things up".
In response, and after prompting from host Jeremy Paxman, Cooper admitted that New Labour should have implemented tighter controls on eastern European migration.