The Government’s new Mansion Tax may affect more than the annual cost of owning an expensive home. It could influence property values, negotiations and the legal arrangements required when buying or selling.

If you own, are selling or are considering buying a property worth £2 million or more, the Mansion Tax deserves attention now, not simply when the first bills arrive in 2028.

The Government has confirmed the framework for its High Value Council Tax Surcharge (HVCTS), and the Finance Bill 2026–27 is now before Parliament. What began as a relatively straightforward proposal for an additional annual charge has developed into a more substantial framework involving valuations, ownership arrangements, deferred liabilities and enforcement.

Perhaps most significantly, the Office for Budget Responsibility (OBR) expects the surcharge to influence property prices and transaction volumes. For buyers and sellers, that may prove more important than the tax bill itself.

What has the Government decided?

Following a consultation involving 424 responses, the Government published its response on 28 October 2026.

From 1 April 2028, owners of qualifying residential properties in England will pay an annual surcharge, additional to ordinary Council Tax.

Charges will increase with CPI from 2029–30. Properties will be revalued every five years, beginning in 2033.

The Government has also confirmed a 100% premium for qualifying properties left substantially unfurnished and unoccupied for at least twelve months, together with exemptions and discounts for certain property categories.

Importantly, liability will generally fall upon the legal owner rather than the occupier. That distinction has particular implications for leasehold properties, companies, trusts and jointly owned homes.

Could Mansion Tax reduce property values?

This is perhaps the most “interesting” aspect of the proposals.

The OBR’s published costing assumes that, over time, the annual surcharge will be reflected in the prices purchasers are prepared to pay. Economists describe this as capitalisation: where an ongoing financial obligation influences the underlying value of an asset.

The OBR assumes eventual full capitalisation of the discounted future tax cost. It also anticipates prices clustering immediately below the £2 million, £2.5 million, £3.5 million and £5 million charging thresholds.

That does not mean every affected property will fall in value by a predictable amount. Prime residential property is not a uniform market. Location, condition, scarcity, financing costs and purchaser circumstances all influence pricing. Nevertheless, the prospect of an additional recurring liability may become part of negotiations, particularly where properties sit close to a threshold.

The OBR also modelled a 1.5% reduction in transaction volumes while valuation uncertainty persists.

These are modelling assumptions, not guaranteed market outcomes. But they illustrate why purchasers, sellers and agents should not treat the surcharge as entirely separate from property values.

There is a further important distinction: the agreed purchase price will not, by itself, determine the surcharge band.

The initial valuations will be based on April 2026 values, using comparable transactions, property characteristics and professional judgement. Negotiating a purchase from £2.05 million to £1.99 million will not automatically remove a property from the surcharge.

For properties approaching a threshold, reliable valuation evidence may therefore become particularly valuable.

The conveyancing implications

The consultation response confirms that legal ownership, rather than occupation, will generally determine liability.

Joint owners will be jointly and severally liable. Companies will be responsible where they own properties, while trustees will be liable for property held on trust.

For long leaseholds, liability will generally fall upon the leaseholder where the lease was originally granted for more than 21 years, regardless of how much of that term remains. This creates potential complications where a valuable flat is held under a diminishing lease, particularly where the value of the leasehold interest differs substantially from the value of the underlying property.

The Government has acknowledged concerns about particular leasehold arrangements, with further detail expected.

Another important issue concerns deferred liabilities. Qualifying households with annual income of £35,000 or less, savings of £16,000 or less, or a household member meeting specified disability criteria will be able to defer payment.

However, deferred does not mean extinguished. The Finance Bill expressly contemplates interest-bearing deferred payment agreements and security which may be registered to protect the outstanding sums. The detailed requirements remain subject to regulations.

Consider a property whose owner has deferred payment for several years before deciding to sell, or where executors are selling following the owner’s death. The accumulated liability and any associated security may need to be addressed before or at completion (like another mortgage). This raises questions about pre-contract enquiries, contractual apportionment, evidence of payment and the discharge of registered security.

The precise conveyancing procedures have not yet been established, but the importance of investigating the position is already apparent.

Why not simply reform Council Tax?

Council Tax was introduced under John Major’s Government in 1993, with English properties divided into eight bands based on April 1991 valuations. That structure remains largely unchanged.

An additional banding system, or a comprehensive revaluation, might arguably achieve similar objectives without creating a separate charge.

However, wholesale reform would affect millions of homes, whereas the HVCTS allows the Government to target a comparatively small proportion of properties.

There is also a geographical difficulty. Allowing authorities simply to retain additional receipts from expensive homes could disproportionately benefit wealthier boroughs. A national approach allows the Government to consider distribution according to wider local-government funding needs.

Whether the surcharge proves preferable to broader Council Tax reform remains an open policy question.

For property owners, however, its practical implications are considerably more immediate.

The dates to put in your diary

Several milestones now deserve attention:

• April 2026: The reference date for initial property valuations
• Autumn 2027: Draft valuation bands are expected, allowing owners to identify potential errors.
• March 2028: Local authorities are expected to issue the first bills.
• 1 April 2028: The surcharge takes effect.
• 1 April 2033: The first scheduled five-year revaluation.

The consultation envisages an initial eight-month period for formally challenging banding, followed by six-month windows for newly liable owners and certain subsequent assessments. The final procedural rules remain subject to legislation.

For owners of properties near the relevant thresholds, autumn 2027 may be the more important date. That is when proposed valuations should become visible and opportunities to correct factual inaccuracies can arise before the system goes live.

Looking ahead

The Mansion Tax introduces more than another annual ownership cost. It establishes a separate valuation framework and new liabilities which may affect purchasing decisions, ownership arrangements and future disposals.

For anyone considering a high-value property transaction, the sensible course is to understand those implications now, rather than dealing with them under the pressure of an impending exchange or completion.

The precise detail will continue to develop, but the direction is increasingly clear. In property transactions, knowing what you are buying has always mattered. Understanding the liabilities accompanying it will matter just as much.

How Edwin Coe can help

Buying, selling or restructuring ownership of a property worth £2 million or more?

The High Value Council Tax Surcharge introduces new considerations which should form part of your property planning well before April 2028.

Charlie Davidson, Senior Associate in Edwin Coe’s Property team and a Legal 500 Leading Associate in London residential property, advises on high-value and complex residential transactions.  Whether you are acquiring a home, disposing of an existing property or considering how the new surcharge may affect your transaction, Charlie can advise on the property law implications and work alongside your tax and valuation advisers.

Contact Charlie Davidson at Edwin Coe to discuss your requirements.

Disclaimer: This article is intended for general information only and does not constitute legal, tax or valuation advice. It reflects Government policy, consultation responses and the Finance Bill as introduced, available as at 9 November 2026. The legislation remains subject to Parliamentary amendment, and detailed arrangements concerning appeals, deferral, security, exemptions and enforcement remain subject to further regulations and guidance. Readers should obtain independent professional advice concerning their individual circumstances.