Angela Rayner has joked she does not want to become Prime Minister because of the toll the job would take on her age.
The Deputy PM - who has previously ruled out running for the leadership should a vacancy arise - also sought to reassure people after a bruising week for Keir Starmer's government of a watered-down welfare bill.
It came as Ms Rayner was told by ITV's Lorraine on Wednesday morning that Keir Starmer "looks tired, he looks under siege" and "absolutely exhausted".
But the senior Labour figure replied: "Even before I was in politics I said that have you ever seen a Prime Minister after a year or two in government.
"People always say to me 'do you want to be Prime Minister'? Not a chance it will age me by 10 years within six months.
"It does anyone - anyone who has been Prime Minister - it is a very challenging job. To be fair for Keir Starmer there has been a lot going on, he's been all around the world trying to repair the relationships in Europe.
"We've got the trade deals the previous government wasn't able to do, tackling the things like the tariffs the President in the US wanted to put on the UK, which would have damaged our economy again. There's a lot going on and the Prime Minister's been here, there and everywhere doing the job for Britain."
Pressed on whether she would like to become PM at some point in the future, Ms Rayner replied: "No."
She added: "To be elected as an MP from my background was incredible. When I first went into Parliament, I thought 'this is Hogwarts, this is an incredible place'.
"But having that opportunity to serve my community that has raised me, looked after me, given me opportunities. And to be Deputy PM of this country it has got to count for something. Not a title but what are you going to give back to your communities and that's why I'm so passionate about council housing that we need... "
The Deputy PM also sought to reassure people who had been "scared" about the proposed overhaul of disability and sickness benefits.
READ MORE: Welfare bill passes crunch vote after dramatic PIP U-turn - what you need to know
After a major U-turn on the welfare bill last night and chaotic scenes in the Commons, Ms Rayner said "welfare reform is always difficult". Speaking to ITV's Lorraine, the Deputy PM said: "Anyone listening to your show today, they know that there will be no changes to their welfare.
"I want to make sure that people are reassured by that, because a lot of people have been scared about what's going to happen." She said: "The future the criteria [for PIP] will be co-designed with disability groups."
But she refused to drawn on how the government's next step as experts warned the reversal of the policy could lead to tax rises at the Budget.
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