"Just yesterday one of Britain's most prominent Right-wing leaders, a man named Nigel Farage who stoked anti-immigrant sentiment to have Britain win the referendum to leave the European Union, campaigned with Donald Trump in Mississippi," she said. "That's who Donald Trump wants by his side when he is addressing an audience of American voters."

Mr Trump dismissed her efforts to portray him as racist as the "oldest play in the Democratic playbook".

He has been attempting to reverse course on immigration this week.

After making the deportation of all 11 million illegal immigrants currently in the US a centrepiece of his primary election campaign, Mr Trump has now signalled he would allow many such individuals to stay in the US.