@MarbleHunt I think that's a much better ground to be debating policy on, i.e. what should a decent society fund, what is the return on different types of spending, what are the trends in spending and impact on the total.
We agree we go wrong when policy debates are rooted in misperceptions. This board shows many (most, maybe) people arguing on the grounds that it costs the public nothing extra for a disabled person to buy a car via Motability vs directly, or to buy a more expensive Motabilty car vs a less expensive one.
Regardless of whether that extra is good or bad, it's just false that there is no extra cost.
VAT on Motabiltiy is nil because of a special rule for the scheme. That's different from normal VAT rules where only substantially modified cars benefit. IPT is also nil for Motabiltiy cars, vs full rate for a disabled person buying normally.
These are worth several thousand pounds per car on top of the allowance.
This is why it reminded me of the pension debate. No, NI does not fund the state pension. Similarly, a not-obvious subsidy. You see a parallel with Brexit. I think that using duff figures is unhelpful regardless of what debate, or what side you. Good debate is something like: "we think £1 spent on Motability renders £x in public benefit. Is that multiple still favourable when talking about the marginal subsidy of a luxury car versus a standard one, or are there other areas of public services that would do more with that money?
I suspect the public benefit of subsidising the luxury over the standard car is no longer a good way of spending public funds, versus other options.
(I looked up public spending on disabled people, which grew from 0.2% in 1985 to 1.6% this year, per OBR. So a seven-fold increase. I'm sure there are many reasons, including ageing, but it's not static at all. Where are your figures from?).
https://obr.uk/forecasts-in-depth/tax-by-tax-spend-by-spend/welfare-spending-disability-benefits