@AIBUYESYES I ignored the £1 million limit because it is irrelevant. The real problem stems from the is the annual allowance of £40k for pension contributions, even deemed contributions, which also applies.
If the actuarial value of the pension pot increases from £400k to £480k in a given year, then there is a deemed contribution of £80k. £40k of that is therefore in excess of the annual allowance, and hence subject to immediate taxation at a rate that is likely to be 45%. So £18k in tax. Due immediately. Bang.
In contrast, a private sector worker who starts the year with a DC pension pot of £400k that increases to £440k thanks to market action, and then increases to £480 thanks to £40k in new contributions, so precisely the same value uplift, faces no excess tax charge, because the market action is not taxed.
That is despite the fact that the market action on the DC pot is a real increase in real money (just tax sheltered), whereas the £480k for the NHS consultant is an actuarial estimate of present value. It could end up being worth less or more.
Note, I am ignoring the effects of inflation here in order to simplify, but on balance that does not help very much, and if anything it could make things worse.
I acknowledge that a private sector worker with a DB pension could theoretically face the same problem, but any decently run company would allow its DB pension plan members ways to avoid this pension trap by reducing their accruals, perhaps reducing extra taxable cash income instead, which would be taxed fairly at the normal rate, but only once, unlike the NHS deemed pension contribution which ends up getting unfairly taxed twice at full whack to the extent it goes over £40k.
Just as an aside, £40k sounds like a huge sum, but the way it is calculated, if your annual pension entitlement goes up by £2.5k then it gets treated like £40k in income in that year. However, if you later convert that to a lump sum, however, it is suddenly only worth £30k before tax. Go figure.