There's an upper band beyond which the tax rate is fixed regardless of how much the property cost in '91.
Also, see the above poster's comment for an example table:
https://www.cambridge.gov.uk/council-tax-bands-and-charges
A 200K (assessed in '91) property pays about 2.5x what a 40K (assessed in '91) property does. Not 5x.
There's an upper band beyond which the tax rate is fixed regardless of how much the property cost in '91.
Also, see the above poster's comment for an example table:
https://www.cambridge.gov.uk/council-tax-bands-and-charges
A 200K (assessed in '91) property pays about 2.5x what a 40K (assessed in '91) property does. Not 5x.