David Cameron's spokeswoman said the government "will not tolerate intolerance" after a series of racist incidents were reported following the Brexit vote.
"We should be absolutely clear that this government will not tolerate intolerance intimidating migrants, telling them they need to go home," his spokeswoman told journalists.
The Polish Embassy in London earlier said it was "shocked and deeply concerned" by incidents of abuse directed at the Polish community.
They include the posting of laminated cards reading "Leave the EU - no more Polish vermin."
London mayor Sadiq Khan yesterday placed the city's police force on alert following the incidents. Khan said he took "seriously my responsibility to defend London's fantastic mix of diversity and tolerance."
John O'Connell, from anti-racism group Far Right Watch, said they had recorded over 90 incidents in the last three days, ranging from "verbal abuse up to physical violence."