Every property in a local authority area is placed in a valuation band, labelled from A (the lowest) to H (the highest) (or A to I in Wales), depending on its value. The higher the band, the more council tax you are liable to pay.

In England and Wales, dwellings are valued by the Valuation Office Agency (VOA; www.gov.uk/government/organisations/valuation-office-agency ; 03000 501 501 (England); 03000 505 505 (Wales)), and in Scotland by the local assessor ( www.saa.gov.uk ). These bodies also decide what counts as a dwelling and how many dwellings there are in a property.
LGFA , Ss.5(2)-(3) & 74(2)

You have the right to challenge the valuation of your dwelling if, within six months, you have become newly liable for council tax there (eg through moving) or if there has been a reduction in its value (eg through partial demolition or its adaptation for use by a disabled person). You can also ask for a change if part