Appendix II: Methodological summary
To estimate the number of UK homes subject to a mansion tax in 2016-2020, Cebr had to estimate:
Current property values of homes in the UK
Changes in regional house prices up to 2020
Average national house prices up to 2020
In order to create the ‘nowcast’ estimates of current property values Land Registry’s “price paid” data
was used. When estimating the current value of London properties borough level data was considered.
To estimate the value of homes in Wales regional numbers were used, while for all other regions
constituency level growth rates were considered.
Since the Land Registry dataset only covers residential properties bought in 1995 and later, the resulting
figures had to be scaled up to the full size of the dwelling stock. When scaling the figures, ONS data
regarding the total stock of dwelling was used for all regions save Wales. In the case of Wales, the total
stock of dwelling figure was taken from the Knowledge and Analytical Services of the Welsh Government.
To estimate the changing number of homes subject to the mansion tax post-2016, the £2m threshold
was increased by the projected growth in high-value homes. This rate was determined based on Knight
Frank’s Prime Central London house price index and adjusted for negative impact of the mansion tax on
property prices. The reduction in prime property values was assumed to equal the average annual
mansion tax payment. The change in property values was estimated on a regional basis to assess how
different parts of the UK would be affected by a mansion tax over time.
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