Chuka Umunna has accused Boris Johnson of saying and doing “racist” things, but did not go so far as to call him a racist.
The Liberal Democrats foreign affairs spokesman said Mr Johnson was unfit to be Prime Minister, and had chosen to align himself with "right wing, authoritarian nationalists”.
When pressed on whether he thought the Prime Minister was racist, he said: “I think the things that he has said and done are racist. Only he in his heart knows whether he is a racist.”
Mr Umunna also criticised Jeremy Corbyn as doing “things which, arguably, amount to anti-Jewish racism”.
“He has allowed anti-Jewish racism to proliferate in the party, the Labour Party, during his leadership,” he said.
Meanwhile, Mr Johnson has also faced criticism from Tony Blair, who said his Brexit plan was a “fantasy”.
However the former Prime Minister chose not to offer a resounding endorsement of Labour, and said a majority Labour or majority Conservative government would “pose a risk” to the UK.
“Both as majority governments pose a risk. It's just that the chances I think of Labour doing that are - if the polls are right - negligible,” he said.
He said Labour’s aims were laudable, but would be “difficult” to achieve, while the Conservatives believed they could “force people to elect them”.
“Having visited this debacle upon us, which has distracted us from those big issues for over three years, they (Conservatives) now use the distraction as a reason for doing Brexit, not abandoning it,” he said.
In response to Mr Blair the current Labour leader said: “I simply invite all those who are looking at it to recognise what we have put forward is a sensible costed plan of how we can improve public services and life opportunities in this country.”
In October Mr Blair told talkRADIO he would “struggle” to back the Labour Party as he had a “profound disagreement with the Corbyn leadership”, and he understood why some had shifted support to the Liberal Democrats.
“I can understand why the people I know in the same constituency as me who will be voting for Chuka Umunna,” he said.
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