Anna Soubry has revealed how Chuka Umunna refused demands to be leader of Change UK before leaving her pained by quitting the fledgling party without a phonecall.
Speaking to for his , she detailed the breakdown of her brief political partnership with Umunna, who she regarded as prime ministerial material but said has proven to have a "history of not stepping up".
In the episode the former Tory MP also lambasted Boris Johnson's leadership credentials, declaring him a "clown on a zipwire" who "couldn't even be trusted to clean the loos".
Ms Soubry said the favourite to succeed Theresa May "has not changed at all, he has learned nothing since he was that terrible foreign secretary", adding: "He's lazy. ... Mendacity runs through him."
The prominent Remain supporter also confirmed she would be willing to back Labour and bring down the government in a vote of no confidence should the next prime minister push for a no deal Brexit.
Ms Soubry had left the Conservatives with two other Tories to join the Labour backbench breakaway in a push to demand a People's Vote on Brexit.
Addressing the breakdown of Change UK, the Broxtowe MP pointed the finger firmly at Umunna, who surprisingly joined the Lib Dems as he quit along with five others last month.
"He should have been our leader and he wasn't. You don't give up at the first hurdle," she said.
"To me (Umunna) was absolutely the future for our country. I genuinely believe that, I wouldn't have left my party if I hadn't believed that."
Ms Soubry said she was particularly upset by the manner in which Umunna left, a move which she only learned about via the news before he sent her a personal email.
"I think he made a terrible mistake (switching to the Lib Dems). I was genuinely really sad about that," she said.
"For me it personally hurt, it really did hurt. I thought he was my big buddy.
"You don't send people an email when you share an office with them or you're just down the corridor, you pick up the phone or you go into somebody's office and say 'mate, we need to have a chat.'"
In the Acting Prime Minister episode, in which guests are offered the hypothetical keys to Number 10, the former barrister explains why French President Emmanuel Macron would be the first person she'd call in power and why "putting the country first" would stop Amber Rudd from having a place in her fantasy cabinet.
While listing a number of Lib Dems as friends, she explains the red lines which would prevent her ever joining Umunna and others to sit with the Lib Dems in the Commons chamber and also addresses the failures she sees in Jeremy Corbyn's Labour party.
But returning to the Brexit saga, she confirms that she wouldn't rule out helping to form a government of national unity, saying: "Nothing is impossible in this crisis."
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