Ok so again thanks for that link, so I see now in black and white on gov.uk that it is not really tied to crown estate profits or reflecting how well the economy was performing, as Osborne actually said at the time, here:
Normally the size of Sovereign Grant for a given year is equal to a prescribed proportion (initially 15% and since 2017/18 25%) of The Crown Estate’s profit for the financial year two years prior to the year in question. This means that the Grant can be set firmly at the beginning of each financial year, Under the requirements of the Sovereign Grant Act 2011, in the event of a reduction in The Crown Estate’s profits in the reference year as in 2020- 21, the Sovereign Grant is set at the same level as the previous year.
and from the article:
If the crown estate profits dipped, the Treasury was legally required to top up the shortfall to ensure that, at a minimum, the monarch would be paid the same as the preceding year. This clause has kicked in twice, ensuring that in the two most recent rounds of public funding, the Treasury has topped up the amount of money being given to the monarchy with an extra £27m over the two years.
If they do not spend it all, they can keep it tucked away.
A pp tried to claim they were being generous by reducing the percentage they're taking, but since it was originally 15% even that's not really accurate or the full picture at least.
Honestly this is all so so disgusting.