A note for people not familiar with the UK: £60,000 per year is about twice the median pay for a full-time worker, so the definition of 'middle class' used here (at least in the headline) is pretty tendentious.
Also, the "Tax Payers Alliance" is an opaquely-financed group with zero membership, which has existed for decades for the sole purpose of getting cited as a 'low tax pressure group' when newspapers feel the need to get 'the other point of view' for some story. Being an astroturf group obviously doesn't make it wrong in any given case, but it has neither a reputation for honesty, nor for actually being anti-tax (it's very loud about taxes mostly paid by the rich; much more quiet about VAT for example).
The idea of "class" is vague (and slightly offensive) which is perhaps why it is being used here.
In any case, "According to the Organisation for Economic Co-operation and Development, middle class is someone who earns 75 per cent to 200 per cent of the median national income."[0] and, as you say, the median "Equivalised household disposable income of individuals" is £29,900 according to the ONS.[1]
I'm not sure if "disposable" here means that the OECD definition doesn't apply, but I agree that the article would have been less misleading if it had used a less subjective term, and a less extreme definition.
It’s important to understand that “middle class” has a very different meaning in the UK than the US. In the UK “middle class” generally means “posh”, you could see it as a shorthand for “upper middle class”.
I think it's probably very contextual. For example, The Telegraph reported that 'Seven out of 10 people view themselves as [middle class]'[0].
That's probably a result both of lower wage people feeling aspirational (and associating "working class" with manual labour) and many people with traditionally upper class traits feeling embarrassed to publicly suggest they are superior.
As the BBC notes, 'David Cameron - educated at Eton - has described himself and his wife - the daughter of a baronet - as part of the "sharp-elbowed middle classes".'[1]
And did you find a job elsewhere that earned you several million dollars per year? Because that's how much you have to earn to pay a million dollars in taxes per year. Especially if you really are just talking about California tax.
If so, congratulations, but you're hardly middle class. You're top 1%, probably top .1%, and few people are in the same situation you are.
Also, the "Tax Payers Alliance" is an opaquely-financed group with zero membership, which has existed for decades for the sole purpose of getting cited as a 'low tax pressure group' when newspapers feel the need to get 'the other point of view' for some story. Being an astroturf group obviously doesn't make it wrong in any given case, but it has neither a reputation for honesty, nor for actually being anti-tax (it's very loud about taxes mostly paid by the rich; much more quiet about VAT for example).