HMRC is preparing to send mansion tax inspectors into homes across the UK to determine whether homeowners should pay more tax under the new levy.

The tax authority will deploy valuation agents who will be able to demand entry to properties in order to assess whether they are worth over £2m and therefore fall under the High Value Council Tax Surcharge – commonly referred to as the mansion tax.

First introduced by former chancellor Rachel Reeves in last year's autumn budget, the levy is due to take effect in April 2028, after a consultation on the new charge ended in July. It will apply to properties worth over £2m, with an extra levy of between £2,500 and £7,500 each year on top of existing council tax bills, contingent on what the properties are worth.

Property owners who refuse to let the inspectors enter their homes may face fines of up to £200 and would be committing a criminal offence, according to The Telegraph.

To determine which homes are subject to the charge, the taxman's valuation agents will use third-party data and information that is already publicly available to estimate the value of properties.

Scope of mansion tax inspections

According to the Valuation Office, the HMRC division responsible for maintaining council tax bands for homes in England and Wales, the inspections will be required where "attributes can only be confirmed internally or a re-measurement is required".

The need for fresh measurements underscores how unusual individual valuations are under the current system: council tax bands in England are still based on 1991 property values, meaning most homes have never been individually revalued since the tax was introduced. Properties worth over £2m are also concentrated largely in London and the South East of England.

The inspectors will conduct assessments of property interiors, including the size and architectural style of homes, whilst also looking at the number of bedrooms, bathrooms, and storeys.

Mansion tax to hit 165,000 homes

The mansion tax charge is expected to affect 165,000 homeowners during its first year, more than the 120,000 originally forecast.

A surplus of 45,000 homes will be hit with the levy, according to the fiscal watchdog, the Office for Budget Responsibility (OBR), with thousands able to successfully appeal the tax. Homeowners in England and Wales can already challenge council tax banding decisions through the Valuation Office and independent valuation tribunals, an established route for disputing how a property has been valued.