She says Mr Johnson is like a "puppy" when he flirts and flatters her as she faces him at Prime Minister's Questions. And she admits he is authentic, even though he is "just an authentic liar".

The Labour leader, on the other hand, is "stable" and "a grown up", but he "over-prepares" for Prime Minister's Questions, his deputy claims in a lengthy profile in the New Statesman magazine.

Ms Rayner's verdict on the character and personality of two main party leaders comes as she speaks of her ambitions to become a Cabinet minister and praises the governments of Tony Blair and Gordon Brown.

Asked how long Mr Johnson has left in Downing Street, she says: "We've got to the point where it's a question of, do you want the edgy, naughty boyfriend, but, actually, in the long run he's toxic?

"Or do you want the stable one who says 'I'm not going to be as racy as that, but I will provide you with a family and nurture you'.

"As a nation, we have to decide. Do we want a grown-up, or someone who's going to throw you in a racing car and thrill you to near-exhaustion and death?"

Comparing herself with the PM, she says: "One of the things the Conservatives fear about me is that I say it how I see it, and that's why the public believed in Johnson.

"You might not agree with what I say, but you know whatever I say is authentic, and people are looking for authenticity. That's what they felt they were getting from Johnson.

"What they're realising now is, he is authentic - he's just an authentic liar."

On her own clashes with the prime minister across the despatch box at PMQs, Mr Rayner says: "You can't beat a puppy so he has to compliment me in a backhanded way.

"I know that he doesn't prepare. I don't think he gets to the dispatch box and thinks, 'I'm just going to lie to the public'. He just spouts whatever comes into his head.

"That's why he comes out with fluffy words that he learned at his school. Whereas Keir over-prepares. He'd never wing it."

Praising Sir Keir's response to being mobbed by a crowd chanting Jimmy Savile slurs outside Parliament, Ms Rayner says: "Keir does not let things like that faze him, He's got a real sense of moral obligation. You can't shake him in that respect."

And on her own relationship with Sir Keir, despite his attempts to demote her after last year's May elections, she adds: "Tom Watson and Jeremy Corbyn had a very different relationship.

"I absolutely believe that Keir would make a brilliant prime minister. Keir has the utmost respect for me in my role. I don't feel patronised by Keir, I never have."

She also shrugs off Sir Keir's distancing himself from her after she described Tories as "homophobic, racist, misogynist scum" at last year's Labour conference, insisting: "He wasn't refusing to defend me, he was just being Keir."

She praises the Blair government for its Sure Start scheme and says of Mr Brown: "He was a pragmatist, able to deliver socialism in a way that was impactful on people's everyday lives. People just saw it as fairness.

"I cannot tell you how transformative the Working Tax Credit was for young girls like me."

And declaring that she is impatient for government, she says: "My biggest regret is that I've been in opposition for nearly seven years.

"I've had to try and convince the government of things that I know are wrong, and I've not been able to do all that we could have achieved. The Sure Start Plus model, for example, is on a shelf. That's our fault.

"Many of our ex-voters blame Labour for Johnson getting in, because they said we didn't give them an alternative. I accept that criticism - you can't say the voters were wrong.

"Hopefully, they've seen that we are different. We are reflective and respectful, and we're going to put forward a government-in-waiting that people can vote for."