I don't know for certain what the process will be that leads to Keir Starmer's removal from Downing Street after next week's local elections. 

Some ministers suspect he will finally see the writing on the wall and walk away. Others believe it will take a leadership challenge to force him out.

But one thing I do know: whatever that process is, it must not end with Angela Rayner as Prime Minister of the United Kingdom.

Yesterday my colleague Christian Calgie reported that Rayner left onlookers 'open-mouthed' at her behaviour in the Strangers' Bar of the House of Commons on Monday night. Some witnesses claimed she had been 'trolleyed'. 

Others that her state of inebriation had led her to walk into a door with such force she had bent over double.

The reports were immediately rubbished by allies. It was all, a spokesman claimed, a 'concoction of mischief making'. It was not.

I was in Strangers' Bar on Monday. I saw Angela Rayner and spoke to her briefly. The description of one witness of her being 'absolutely obliterated' is true.

Her condition was witnessed by numerous MPs, journalists, parliamentary staff and guests. The incident of her walking into a door with force is also accurate. I saw it happen with my own eyes.

In the coming hours, the outright denials from her supporters will be parked. Instead, we will get a series of ritual and well-worn justifications.

Rayner is being targeted because she is a woman. She's being targeted because she's working class. She is being targeted by joyless puritans. 

Angela is a target because she stands on the brink of power, and her political opponents – both inside and outside her party – fear her and want to bring her down.

So let's deconstruct and dispense with each of these false claims in turn.

The Labour Party is packed with women who are not just capable of replacing Keir Starmer, but would almost certainly do a better job. Yvette Cooper. Bridget Phillipson. Shabana Mahmood. Lucy Powell. Heidi Alexander. Gender is not the issue.

Neither is class. Andy Burnham grew up in the Liverpool suburb of Aintree, the son of a telephone engineer and a receptionist. 

Phillipson was brought up by her mother – who worked for a domestic violence charity – in a council house on Wearside. 

Wes Streeting was born in Stepney, and spent his childhood in a council flat with six siblings. So despite appearances, Rayner is not the only Labour politician maintaining the party's tenuous links with its working-class roots.

Equally, few voters will have a problem with a politician who enjoys a drink. Or even one who, in private, gets drunk. Winston Churchill won a world war on a diet of brandy, port and Pol Roger.

But there is both a time and a place. And a Monday night in a busy parliamentary bar – at a moment when you are trying to convince your colleagues you are the person to be entrusted with Britain's nuclear launch codes – is neither.

There was a reason Angela Rayner was in that particular watering hole. The parliamentary estate has numerous restaurants, tea-rooms and hideaways where it's possible for an ambitious politician to discreetly lobby their fellow MPs. 

But Strangers is an open space frequented by members of all parties and – crucially – by members of the press.

It is where aspiring candidates go when they wish to make a point. To signal they are running for a particular office, without explicitly saying so. It is where they go to audition.

The fact Rayner could not pass the audition without falling flat on her face – or in this case face-planting a large wooden door – is instructive. 

As one MP who is not on Rayner's team, but is keeping an open mind about the leadership, said to me: 'Sorry, but it's not good enough. She wants to be leader of the party and the Prime Minister of the country. And she's staggering around in that state. That's not acceptable.'

As Nigel Farage's meteoric rise has proven, people are attracted to politicians who have some character and reject the stuffy and robotic caricature of the identikit Westminster politician. 

But this is not an episode of I'm A Celebrity. The Government and country are approaching a watershed. 

The Labour Party is about to choose a new leader and Prime Minister. And the bare minimum that's required is for the man or woman they choose to conduct themselves with a basic level of professionalism and self-control.

Angela Rayner cannot do that. Her behaviour on Monday was not an aberration. Concerns about her social conduct have been widespread within the Parliamentary Labour Party for some time. 

Which is why her allies recently briefed MPs and journalists that she was avoiding alcohol.

If Rayner was surrounded by advisers with the experience and maturity to safely guide her through the intensity of a Labour leadership contest and a future elevation to No 10, some of these difficulties might be mitigated. 

But the very opposite is true. Many MPs believe members of her inner circle are actively exploiting her, and using her to further their own political ambitions.

Angela Rayner has many qualities. Ones that extend beyond the normal lazy narratives about her earthiness and robustness. 

She has finely tuned political instincts. In her management of the Housing Department – before she resigned last year – she was skilful in circumventing the obstacles placed in her way by the Whitehall bureaucracy.

She still has a lot to offer her party and her country.

But she cannot become Prime Minister. The weight of office would destroy her. The Government would swiftly collapse in a manner reminiscent of the implosion of the Liz Truss premiership. 

Which is why her colleagues, and those who claim to be her friend, have a duty of care to Rayner to ensure that does not happen.

In the past few months, I have chronicled the decline and fall of Keir Starmer. I bow to no one in my steadfast belief it is the interests of his government, party and country that he is removed from office as swiftly as possible.

Which is why I do not say this lightly: if it comes down to a straight choice between Keir Starmer and Angela Rayner, Labour must stick with Starmer.