The high_value_council_tax_surcharge formula applies the charge to English households with a qualifying main_residence_value, regardless of whether they own their home. The announced policy places liability on property owners.

At b5b0923, the formula checks the year, country and property value, then returns the surcharge for every household in England. It never reads tenure_type. Consequently, changing an otherwise identical household from owner-occupied to privately rented leaves its surcharge unchanged.

The Drill 1 evaluation identified this in a mock reform lowering the threshold to £1.5m: approximately 27,100 private-renter households were charged £68m. The dashboard corrected its Personal impact adapter, but the national calculation retained the model’s behaviour. These figures describe the rehearsal dataset and reform, not the current-law population impact.

The fix should:

• Require tenure_type to be OWNED_OUTRIGHT or OWNED_WITH_MORTGAGE before charging the household for its main residence.
• Retain the existing commencement date, England restriction, valuation adjustment and band calculation.
• Apply the ownership condition under both baseline policy and threshold reforms.
• Set tenure explicitly in owner test fixtures: the current default is RENT_PRIVATELY.

Add regression tests showing that:

• Each owner tenure retains the expected surcharge.
• Private, council and housing-association tenants owe zero on their rented home, even with an explicitly supplied property value above the threshold.
• The ownership condition still holds when a reform lowers the threshold.
• Existing geographical, commencement-date and value-boundary cases continue to pass.

Microcosm #1089 now prevents owned main-residence value from being imputed onto renter households. The model should also enforce ownership for older datasets and explicit household inputs.

This issue covers liability on the household’s main residence. Landlord and second-home liabilities require separate property-level ownership and valuation coverage. Removing tenant charges does not transfer those liabilities to landlords or preserve the existing revenue estimate.