Four weeks. That is how long owners of £1.5 million-plus homes have before the Chancellor stands up on Wednesday 28 October 2026 and potentially redraws the line between an ordinary expensive house and a taxable "mansion". As of October 2026, speculation reported by The Times suggests that line could move from £2 million down to £1.5 million, pulling more than 100,000 additional homes into scope. For anyone selling, buying, inheriting or simply living in a higher-value property, the mansion tax threshold decision is no longer background noise. It is a live financial planning issue with a hard deadline.
This article sets out exactly what is confirmed, what is speculative, and what sellers, landlords and owners of higher-value homes should do before and after Budget day.
Before diving into speculation, it is worth separating fact from rumour. The Government has publicly stated there are no immediate changes planned to stamp duty or council tax. That reassurance matters because both taxes affect far more households than any mansion tax ever will.
What is confirmed is the date itself: the Autumn Budget will be delivered on Wednesday 28 October 2026. The Budget will also set out the price caps, income caps and timeline for the new "Your First Home" scheme, announced on 26 September 2026. This offers first-time buyers a route to purchase with a 2.5% deposit alongside a 20% government equity loan, restricted to new-build properties. Details on eligibility thresholds are expected to be finalised on Budget day itself.
The High Value Council Tax Surcharge, commonly dubbed the "mansion tax", was already heading for homes worth £2 million or more from April 2028. Under that original design, annual charges would range from £2,500 to £7,500 depending on value, and the Valuation Office Agency is currently assessing properties. The Treasury has estimated the surcharge could raise £270 million a year from London alone.
The new development reported by The Times is that the Government is considering lowering that threshold to £1.5 million. The effect would be significant:
That is an increase of roughly 106,000 homes being drawn into the surcharge net, even before the policy has come into force.
Tom Bill of Knight Frank made the point directly, noting that if the speculation proves accurate, the Government would be widening the tax net before even introducing the measure. That is an important framing for any homeowner near the boundary. A property valued today at £1.6 million might currently feel comfortably outside mansion tax territory. Under a £1.5 million threshold, it would not be.
The question is not just about which homes get taxed. It is about trust in thresholds generally. A policy announced as applying to £2 million homes, then lowered before implementation, sets a precedent. Owners sitting just below any future line have reasonable grounds to expect it could move again before April 2028.
This is particularly relevant for sellers of £1.5 million-plus homes right now. Buyers negotiating today may factor potential future annual charges of £2,500 to £7,500 into what they are prepared to offer. A property that falls just inside a lowered threshold could see buyer interest soften, even though the surcharge itself will not start until 2028.
Mansion tax is not the only property-related measure under discussion. Senior ministers have called for capital gains tax reform that would:
Combined, these changes are estimated to raise £1.5 billion to £2 billion a year. For landlords and owners of second homes, this is arguably more consequential than the mansion tax threshold itself, since it touches every disposal, not just high-value primary residences. Ending the death uplift in particular would affect estate planning for families who have historically relied on it to pass on property tax-efficiently.
The policy speculation is landing on an already nervous market. Zoopla's 1 October 2026 House Price Index showed UK annual price growth of just 0.8%, with the average property price at £273,000, and sales agreed down 9% year-on-year. At the same time, the 10-year gilt yield hit 5.38% on 30 September 2026, its highest level since 1999, a signal that borrowing costs across the economy remain elevated.
Higher gilt yields typically feed through to mortgage pricing over time. Combined with Budget uncertainty, this is encouraging some sellers of higher-value homes to either act before 28 October or wait for clarity before listing.
If a lower £1.5 million threshold is confirmed, the exact value the Valuation Office Agency assigns to a property will determine whether it falls inside or outside the surcharge band. An independent RICS valuation gives homeowners their own evidence base, separate from automated or desktop valuations, which can be useful if a VOA assessment is ever disputed. For anyone near the boundary, this is not a luxury step; it is a practical safeguard against being wrongly captured by a surcharge designed for higher-value homes.
For buyers currently house-hunting above £1.4 million, the sensible approach is to treat the mansion tax threshold as unresolved and build in contingency rather than assume the current £2 million line will hold. For existing owners, the biggest risk is complacency: a home comfortably below £2 million today may not be comfortably below £1.5 million. For landlords, the CGT reform conversation deserves at least as much attention as the mansion tax headline, given the broader reach of aligning CGT with income tax.
A chartered surveyor or RICS registered valuer adds real value here beyond simple price-setting. They provide a defensible, documented valuation that can support negotiations with buyers, discussions with lenders, and potentially future conversations with the Valuation Office Agency if a surcharge assessment looks out of step with market value.
When is the Autumn Budget 2026?
Wednesday 28 October 2026.
Has the Government confirmed changes to stamp duty or council tax?
No. The Government has said there are no immediate changes planned to either tax.
What is the mansion tax threshold now, and could it change?
The High Value Council Tax Surcharge is due to apply from £2 million from April 2028. The Times reports the Government is considering lowering this to £1.5 million, which would widen coverage from about 165,000 to about 271,000 homes.
How much would the mansion tax surcharge cost?
Annual charges of between £2,500 and £7,500, depending on property value, under the current design.
Is capital gains tax definitely changing on 28 October?
Not confirmed. Senior ministers have called for reform, including aligning CGT with income tax and ending the uplift at death exemption, which could raise £1.5 billion to £2 billion a year, but this remains a proposal rather than confirmed policy.
Why should I get a RICS valuation before the Budget?
An independent valuation gives you documented evidence of your property's value ahead of any threshold change, which can support your position if the Valuation Office Agency later assesses your home for the surcharge.
The run-up to 28 October 2026 is defined by uncertainty layered on top of a few hard facts. Stamp duty and council tax are not changing immediately. The mansion tax threshold and CGT reform are both under serious consideration but not yet confirmed. Meanwhile, Zoopla's data shows a market already cooling, and gilt yields at their highest since 1999 are adding pressure from the borrowing side.
The practical next steps are clear. Owners of homes near the £1.5 million to £2 million range should commission an independent RICS valuation now, review any pending transactions, and speak to a tax adviser about CGT exposure before Budget day. Waiting for full clarity is reasonable for major decisions, but doing nothing to understand personal exposure is not. Whatever the Chancellor announces on 28 October, those who have already done the groundwork will be in the stronger position to respond.
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