The official Government Right to Buy website
Previous discounts – if one or more of the applicants has previously benefited from a discounted sale on another property, either with your current landlord or with another public sector landlord, this will be deducted from the discount amount. If the previous discounted sale was shared, a proportion of the discount they received is deducted for each party who is joining in the current application.
Cost floor rule – Your discount may be reduced by the ‘cost floor’ rule. This may apply if your home has recently been purchased or built by your landlord or they have spent money on repairing or maintaining it.
Your discount could be reduced to nil if the cost floor is more than the value. If this happens, you would pay the full market value for your home.
The cost floor period for council properties is either:
If you are buying under the Preserved Right to Buy, the cost floor period is 15 years regardless of when it was built or acquired.