The UK's proposed High Value Council Tax Surcharge (HVCTS), commonly referred to as the "mansion tax", is already influencing behaviour within the prime property market, despite not being scheduled to take effect until April 2028.

Recent analysis by Hamptons, reported by the Financial Times, suggests that falling prime property values and changing seller behaviour mean thousands fewer homes are now expected to fall within the £2 million threshold than when the policy was announced in the 2025 Autumn Budget.

Rather than remaining comfortably above the proposed threshold, many properties have slipped below it as sellers adapt asking prices to reflect changing market conditions.

At first glance, that may appear to be positive news for owners of expensive homes.

However, the wider story is far more significant.

Whether a property ultimately becomes liable for the surcharge is only one part of the financial planning equation. For many affluent homeowners, property investors and international buyers, the proposals introduce another layer of complexity into decisions around borrowing, refinancing, ownership structures and long-term wealth planning.

The government's consultation remains open until 14 July 2026, meaning the precise operation of the surcharge continues to evolve.

The Tax May Be Changing Behaviour Before It Even Exists

One of the more interesting findings from the Hamptons research is that pricing behaviour appears to be changing well before implementation.

Its valuation model suggests there are around 8,800 fewer properties in England now valued above £2 million than when the policy was announced, with between 1,000 and 1,500 homes moving below the threshold each month during 2026.

This should not come as a surprise.

Property markets have always reacted to tax thresholds.

The previous Stamp Duty "cliff edges" frequently created pricing distortions, with sellers choosing values just below tax bands to preserve buyer demand. A similar pattern now appears to be emerging around the proposed £2 million valuation point.

That does not necessarily mean every seller is consciously avoiding the surcharge. Prime values have softened across parts of London and the South East over recent years, but the existence of a clearly defined tax threshold is inevitably becoming part of pricing discussions between vendors, buyers and estate agents.

What Is The High Value Council Tax Surcharge?

The proposed surcharge was announced in the Autumn Budget 2025 and is expected to apply from April 2028 to residential properties in England valued at £2 million or more using 2026 valuations.

Current proposals include annual charges beginning at:

• £2,500 for properties valued between £2 million and £2.5 million
• Higher annual charges for homes above £2.5 million, £3.5 million and £5 million

Unlike Stamp Duty Land Tax, this would be an ongoing annual charge rather than a one-off tax payable when purchasing property.

Importantly, liability would sit with the property owner rather than the occupier, with HM Treasury proposing regular revaluations and automated valuation models supported by professional assessment where necessary. The consultation is also seeking views on valuation methodology, appeals, exemptions, deferred payment arrangements and potential additional charges for certain overseas owners.

Why Finance Planning Matters More Than Ever

For many affluent homeowners, tax discussions naturally focus on accountants, yet financing decisions can be equally important.

The structure of borrowing, the ownership vehicle, future liquidity requirements and wider investment objectives all interact with taxation.

Many high-net-worth individuals intentionally retain mortgage borrowing even where they could purchase outright because preserving capital can provide significantly greater flexibility for business investment, portfolio diversification or estate planning.

When tax rules change, those financing decisions deserve to be reviewed.

A modest adjustment to borrowing strategy today may provide considerably more flexibility than reacting after legislation has been finalised.

This is particularly relevant where borrowers are already approaching refinancing events over the next two years.

Rather than simply selecting the lowest available interest rate, sophisticated borrowers increasingly assess finance within the context of their wider balance sheet.

Overseas Buyers Face Additional Uncertainty

The consultation has also introduced another area receiving considerable attention within international markets.

HM Treasury is seeking views on whether a further premium should apply to certain non-UK resident owners alongside the High Value Council Tax Surcharge. Although no final decision has been made, the proposal has attracted significant interest among international investors and advisers.

For overseas buyers already navigating changes to the non-dom regime, Stamp Duty, capital gains tax and inheritance tax planning, the possibility of another recurring property charge reinforces the need for careful advice before acquiring or refinancing UK property.

For some international clients, ownership structures that previously worked well may deserve reconsideration.

Valuations Could Become More Important Than Ever

One of the most debated aspects of the consultation concerns property valuation.

Unlike mainstream housing, prime residential property often has relatively few comparable sales. Individual characteristics such as architectural design, conservation restrictions, private land, security features or extensive refurbishment can materially influence value.

The government proposes using automated valuation models supported by professional judgement where appropriate, but advisers have already questioned how consistently unique homes can be assessed.

Properties sitting close to the £2 million threshold could therefore experience increased scrutiny, particularly if owners believe valuations do not accurately reflect market conditions.

Prime Property Finance Is Becoming More Strategic

For Willow Private Finance, the emerging discussion is not simply about another property tax, it reflects a broader trend affecting the prime housing market.

Affluent borrowers increasingly require finance advice that sits alongside tax planning, legal advice and wider wealth management.

Private banks, specialist lenders and high-net-worth mortgage providers have long recognised that lending decisions cannot be viewed in isolation.

Borrowing often supports investment strategy, liquidity management, succession planning and portfolio optimisation rather than simply facilitating property purchases.

As tax policy evolves, those conversations become even more valuable.

Early Planning Usually Creates More Options

No legislation has yet been finalised.

The consultation remains open until 14 July, and aspects of the policy may still change before implementation. However, waiting until 2028 may significantly reduce the options available.

Owners of properties approaching or exceeding £2 million may benefit from reviewing borrowing arrangements, ownership structures and longer-term objectives well before the new rules take effect.

Whether that ultimately results in refinancing, restructuring ownership, raising capital for other investments or simply confirming that no changes are required, informed planning almost always produces better outcomes than reactive decision-making.

For affluent homeowners, the conversation is no longer simply about property values.

It is increasingly about how finance, taxation and long-term wealth strategy work together.