12 Dec 2025
Almost 500 homes across St Albans and Harpenden could be affected by the Government’s new “mansion tax”, new research has revealed.
The mansion tax and revaluation of council tax payments for higher bands announced in Chancellor Rachel Reeves’ Autumn Budget were always going to have a major impact on homeowners in affluent St Albans and Harpenden.
Not-for-profit company Tax Policy Associates modelled the impact of the mansion tax by analysing Land Registry data on every property transaction since 1995, allowing an estimate of how much each postcode and Parliamentary constituency will pay.
It shows 256 properties in St Albans and 193 in Harpenden will be affected, although this can be broken down to show individual areas – for example, 53 in West Common, Harpenden, and 29 in Marshalswick.
Estate agent Steve Walker, owner of Collinson Hall, said a lot of the details relating to the new tax were still unclear, but offered an insight into how it would work.
“My understanding is that the ‘mansion tax’ (officially the High Value Council Tax Surcharge) will be a recurring annual surcharge added on top of normal council tax. It would appear that the legal owner(s) of the property will pay it, not necessarily the occupier/tenant.
“The tax is due to come into force in April 2028 and any home with a market value of £2 million as of April 2026 or more will be in scope.
“Based on the Budget guidance so far, the surcharge has four value bands.
- £2.0m – £2.5m: £2,500/year;
- £2.5m – £3.5m: £3,500/year;
- £3.5m – £5.0m: £5,000/year;
- £5.0m+: £7,500/year.
“So if your home is valued at, say, £3.2m, you’d pay your normal council tax plus £3,500 each year. Local authorities/VOA-style assessors will likely use comparable sales evidence, with professional judgement for unique homes, and there will be an appeals route with details to be confirmed in secondary guidance which no-one has seen yet.
“St Albans and Harpenden will have a significant number of homes that will be impacted. In particular there will be plenty of homes that sit around the level of the threshold and these will inevitably see disputes registered against the tax.
“For instance, if a ‘desktop valuation’ method is used to assess the value, comparable evidence drawn from Land Registry, EPC data or property portals will inevitably contain significant inaccuracies and the whole system will get bogged down in the time and expense of administering an appeals process.
“For instance two similar houses on the same street can have different values by virtue of their outlook and/or proximity to a railway of a beautiful lakeside view. That kind of valuation influence is not measured by Land Registry or the portals and can be very subjective.
“Also Land Registry information does not include square footage so most desktop valuation models rely on information from EPCs. But as these were only required on property sales since 2007 there will many homes that have not had one.
“For people who are asset-rich but income-poor (eg retirees in expensive areas), the annual nature probably matters more than a one-off tax; there may be political pressure for deferral/relief schemes, but none are confirmed yet in the Budget documents and this may not be something that the present Government would entertain.
“Clearly a lot lies in the detail of how the scheme is implemented.”
St Albans MP Daisy Cooper has also responded to the measures: “It’s no secret that the property tax system in this country is broken. From council tax, to stamp duty and business rates, all three taxes are outdated and create distortions in behaviour. But the Government’s so-called mansion tax won’t fix this.
“Economists from the political left and right, from Paul Johnson of the IFS to Tax Justice UK, have all said that the Government’s proposals for a mansion tax and revaluation of the three highest council tax bands are effectively a badly thought through, messy compromise.
“It will only raise £400 million, which isn’t very much in Government terms, and will cause bunching of house prices under the thresholds.
“If the Government was serious about going after wealth, they would reform capital gains tax in a way so that it was fairer.
“They’d be looking to go after a levy on windfall tax on the big banks which could raise £30 billion in the next five and a half years and go after people like Elon Musk who are making billions of pounds whilst refusing to make social media sites safer for our children.”
Harpenden MP Victoria Collins added: “With some of the highest house prices in the country, homeowners in Harpenden will be impacted by the Government’s mansion tax, which is riddled with complications, unintended consequences, and will fail to raise any significant amount of money.
“This policy will do nothing to fairly reform the broader property tax system – including council tax, stamp duty and business rates – whilst slowing down the market at the top end, not least because of contested valuations, having a knock on impact on the rest of the housing market.
“I completely understand the need to invest in improving our public services. That includes growing our economy with a better trade deal with Europe as Brexit has left a hole of £90bn a year in our public finances.
“That’s also why I support the Liberal Democrats call for an increase to the Digital Services Tax on tech giants from two per cent to 10 per cent to raise an extra £4 billion a year and a windfall tax on the big banks that could raise £30 billion by 2030 – targeting the huge multinational corporations that have been seeing eye watering profits without paying their fair share of tax rather than family homes.”
Maps by OpenStreetMap contributors. Contains HM Land Registry data © Crown copyright and database right 2025. Produced by Tax Policy Associates.
