Boris Johnson has "said and done" racist things, Liberal Democrat candidate Chuka Umunna has said.
In a stinging attack on the Prime Minister, Mr Umunna said Mr Johnson was unfit to be PM and accused him of aligning himself with "right wing, authoritarian figures" on the world stage.
Asked if he thought Mr Johnson was racist, the Lib Dem Cities of London & Westminster candidate said: “I think the things that he has said and done are racist.
“Only he in his heart knows whether he is a racist.”
In a wide-ranging speech, Mr Umunna - who left Labour earlier this year - also criticised Jeremy Corbyn.
He said: "And likewise with Jeremy Corbyn, Jeremy Corbyn has done things which, arguably, amount to anti-Jewish racism.
“And he has allowed anti-Jewish racism to proliferate in the party, the Labour Party, during his leadership.”
Speaking in Watford, Mr Umunna said he was not surprised by the “squeeze” the Lib Dems had received in the polls, but insisted voting for the party was the only way to stop a Tory majority.
Mr Umunna said Mr Johnson would be US President Donald Trump's "poodle" if he wins the election and takes the UK out of the EU.
The Lib Dem said: "Not only will we cease to be that important bridge between the EU and the US but by withdrawing from the European Union, inevitably Johnson will become more reliant on Trump in the short term if he is re-elected.
"Johnson is desperate to secure a US trade deal to make up for the damage done to our global standing if Brexit happens.
"From my own contacts with the US government, it is clear a high price will be demanded and close alignment with US rules and regulation demanded - we risk becoming a vassal state of the US if Boris Johnson gets a majority.
"Leave the EU and the UK under Johnson will become President Trump's poodle. That is what is at stake at this election."
Mr Umunna said that under his party's plans the defence budget will be almost £1 billion bigger in 2024-25 than under the Tories.