Despite your feelings on the issue, the difference is quite stark. Relying on allocations in yearly budgets, subject to the political whims of lawmakers, is clearly a different animal altogether.
During renegotiation, sure Parliament can opt not to renew. But for the duration of the charter, the BBC has an uninterrupted period of collections beyond the fiscal year of the government, which cannot be raided to fund the new social program of the day.
Couldn't the Parliament negotiate with BBC to allow them funding of XY pounds per citizen. Amount to be transferred monthly from the taxes.
It would have the same effect. For the duration of the charter, BBC would be guaranteed funding without interference from the government. Only difference is method of collection and in my view, reduced cost of collection.
Wouldn’t be much of a Royal charter if the BBC became an Office of the Government.
If you are an agency which wishes to retain some modicum of control over your own destiny, then you most likely wish to retain some modicum of control over your sources of revenue.