Labour's Shadow Foreign Secretary branded Boris Johnson a 'reckless liar' surrounded by 'Rasputin-like' cronies on BBC Question Time.
The withering attack took place at the end of a humiliating day for Mr Johnson, whose brother earlier resigned as an MP.
Emily Thornberry slammed the Prime Minister for his handling of Brexit on last night's Question Time - and also hit out at his strategy guru Dominic Cummings.
She said: "I shadowed Boris Johnson for two years I knew how bad he was going to be as Prime Minister, well at least I thought I did.
"I think that this man has no judgement and most important of all he is determined to drag our country out of the European Union without a deal.
"He's reckless, he's a liar, he certainly isn't in the interests of this country.
"Until recently people have acted in accordance with rules and have accorded to the law and haven't played games and haven't had slightly sinister Rasputin-like creatures in No.10... and I'm thinking about someone called Cummings who's not even a member of your party but who seems to be pulling all of the strings."
The MP faced severe criticism on Twitter for branding the Prime Minister a liar, although some users rallied to her defence.
James wrote: "She’s right. Johnson is not fit to lead the country. His old boss thinks that. His brother thinks that. His ex campaign manager thought that."
However, Charlotte Gill tweeted: "Emily Thornberry describes Downing Street figures as being like "Rasputin"!
"So Brexiteers have had: Hitler, ISIS, apartheid and now Rasputin.
"The offensiveness of these comparisons aside, can Remainer extremists make up their mind who they want to demonise us with?"
Boris Johnson pleaded with brother Jo, who supports a second referendum on Brexit, not to quit in a desperate phone call, it has been claimed.
The Prime Minister is said to have urged his brother to sleep on it and reconsider his decision, in a lengthy conversation on Wednesday night.
The departure is a severe blow to Boris Johnson at a time when he’s alienated the moderate wing of his party by expelling 21 MPs on Tuesday because they voted against the Government.
