Research reported by the Financial Times says valuations used for England’s “mansion tax” may be at risk because a substantial share of high-value homes lack comparable sales data. The report states that around two-fifths of properties valued at £1.5 million or more do not have sale records in the UK Land Registry, leaving less information to support accurate valuation estimates. In practice, the policy relies on property valuations that can be informed by registered transaction data, and missing records can make it harder to benchmark values or validate assessments. The finding points to a data gap that could affect how some homes are assessed for the tax and may increase uncertainty around the valuation process for specific properties. The article frames the issue as a methodological challenge rather than a claim about individual cases, citing the scale of the missing records among eligible high-value homes. Overall, the reporting highlights concerns about data completeness as a factor that can influence valuation reliability under the scheme.