Keir Starmer is the son of a toolmaker. You will likely already know this because he’s told us. He’s told us time and again.

It is in Sir Keir's interests to hammer home - I wish that pun was intentional - his solidly working class roots. His father was a toolmaker, his mother was a nurse, he lived in a pebbledash semi, he shared a bedroom with his brother.

I have heard these things so many times that I don't have to Google them to check; they are ingrained in my mind and that is a PR job well done.

This is his "humble origins" story. He understands the plight of the working man because he slept in bunk beds as a boy.

The Venn diagram of Keir Starmer and Posh Spice might have a slim centre, but the leader of the opposition finds a kindred spirit in Victoria Beckham.

Mrs Beckham now finds herself recreated as a meme thanks to an awkwardly endearing scene in the Netflix documentary about the couple, Beckham.

In it, the singer describes herself as being from a "very working-class background" before her husband intervenes and very gently but persistently coaxes from her the fact that this is nonsense.

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"Be honest," he says. "What car did your dad drive you to school in?" After some hesitation, his wife replies: "In the eighties, my dad had a Rolls-Royce."

Beckham, satisfied his work is done, nods and closes the door.

It is a perfect encapsulation of the dispute on what constitutes working class, what does not, and how people feel about the issue.

Keir Starmer requires to claim some kind of working-class identity to show he has a connection to a portion of the electorate Labour must woo back, a demographic alienated in the Blair era.

New Labour under Blair made itself available to a particular type of aspiration that normalised support for things that would have been an anathema previously: private schooling and private landlords, say. Sir Keir wants to return Labour to its roots as a party in support of the ordinary, working man - whatever it means to be "ordinary".

Victoria Beckham understands that is has become unfashionable to lay claim to a comfortable, middle-class childhood. It is, dare I say it, fashion to claim a working-class origin story.

The actor Benedict Cumberbatch once described - through crocodile tears - how dislike for the upper classes was the last acceptable prejudice and he was right, albeit no one felt sorry for him.

We live in a time where it is preferable to be able to outline a personal struggle, of any sort, as though we are all competing for sympathy votes on a mass reality TV show.

And it is offensive when people do this because "working class" and "struggle" are not synonymous.

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There is a fallacy that being working class automatically extends to enduring certain social issues - addiction, abuse, homelessness, financial misery - whereas the reality is often more prosaic.

Sometimes there is precarity in being working class - a delay to a paycheck could spell disaster. Sometimes there is not. My grandfather was the foreman in an iron foundry, my grandmother left school at 14 and was a housewife. None of their three daughters would describe hardship in what was an unarguably working-class household, which is, I think, the reality for many, that resources are not ample but are sufficient.

But class is now an issue of identity and, as such, goes in phases. Identity is not a concrete but a viscous thing and so traditional class markers have become fluid and, oftentimes, meaningless.

One of the biggest class changes in recent decades has been the shift away from being defined by one's class to defining one's own class.

A Rolls-Royce is one person's fancy trapping and another person's cheap runabout. This is why people become distressed about taxes: the majority of us will always feel we need more money and that other people are richer than ourselves.

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This lack of clarity was why, in a deeply awkward interview this week on LBC with Nick Ferrari, Sir Keir was entirely unable to define what he meant by "working class".

"Working class is families that work for their living and earn their money through going out to work every day. Working class has the hope to get on in life." Ferrari, of course, pointed out this could just as well apply to middle-class families.

The opposition leader tried again, saying he "was addressing a particular thing with working-class families, which is this sense that - I was talking about the nagging voice that many families have - that 'this isn't for you', 'this isn't for me' - and I think that holds people back."

His voice, wobbling now like the sound of a turkey's gobbling, went on: "That is the ordinary hope of the working class, which is to have a decent education, to get a decent, secure job, to get a car, to have a nice holiday."

To try and circumvent this confusion, Labour parlance more usually references "working people" instead of "working class", which falls down immediately. It is more obviously measurable but still meaningless.

Prince William would, after all, be described as such. A person relying on Universal Credit would not.

Where else do you go for a definition? Some people will rely on it being what one has, others on what one does. Some people will claim to remain working class if they were in childhood, despite having clearly crossed the Rubicon to the middle.

These people are sometimes disparaged as imposters, rightly. But class matters in material yet also unmeasurable ways. It is very difficult, say, to explain to someone who has had a comfortable upbringing just how intimately a financially straitened childhood haunts your life and decisions, how every penny is counted and how destabilising dreadful financial threat feels.

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It is helpful for politicians that the definition remains vague. Both left and right can use "working class" to signal a sort of nobility or righteousness without having to pin down what it really means.

Notions of class form key components in Labour's tilt at the red wall seats and in the Conservative bid to turn issues it believes the working class to be interested - immigration, chiefly - into culture war battles.

On the right, the assumptions about working-class views are offensive: that working-class people are anti-immigrant and anti-green policies. On the left, Starmer's support for the working person rings hollow. The party conference in Liverpool was awash with big business while Jim Murphy, former Scottish Labour leader, said Keir Starmer’s administration will be the “first private sector government in Labour’s history".

This would be the point to share my own definition of working class but, like Sir Keir, I don't have one. Still, he can't define "working class" but, a hint to him, he can stop patronising it and that would be a decent start.