In July 2015 the Chancellor announced a technical-sounding change — Section 24 of the Finance Act, restricting the mortgage-interest relief landlords could claim. A decade later it has done something few tax measures achieve: it rewired who owns Britain’s rental housing. The clearest evidence of that is not a public statistic — it is the shape of GalimAI’s own database, where company ownership is now the norm. This study uses that proprietary map to show what Section 24 built and, more usefully, who it leaves most exposed today.
What GalimAI’s own data reveals
The incorporation boom is not an abstraction in GalimAI’s data — it is the dataset itself. The overwhelming majority of the 463,022 property-owning companies GalimAI maps across England and Wales are exactly the vehicles Section 24 made attractive: limited companies and special-purpose vehicles holding rental property, each created so that mortgage interest stays a deductible cost. GalimAI links every one of them to the people behind it, so the boom is visible not as a headline but as more than a million named owners attached to nearly half a million companies.
That linkage is what makes the data unique. Public records can tell you a company exists; GalimAI’s map tells you who controls it, how many properties it holds, how it is financed and whether it is showing strain. Our own analyses trace the patterns Section 24 set in motion — the SPV flipper pattern, the wave of new buyer companies formed in 2025, the rise of family-owned property companies using incorporation for succession, and the owners most active in the last 24 months.
For an investor that is the practical payoff. The owners most exposed to Section 24 — higher-rate landlords with geared, individually-held portfolios who have not yet incorporated, and over-leveraged SPVs feeling the tax and higher interest rates together — are not a statistic in GalimAI but a reachable list of named owners, each attached to the property they hold and the way they have financed it.
What changed: Section 24, in plain terms
Section 24 was announced in the Summer Budget of July 2015, phased in from April 2017, and reached full effect in April 2020. Before it, landlords deducted mortgage interest as a business cost. After it, individual landlords can no longer deduct finance costs from rental income — they receive only a flat 20% tax credit instead.
Crucially, it bites on individuals, not companies. A limited company still deducts mortgage interest as an ordinary expense and pays corporation tax only on what is left — which is why incorporation became the standard response, and why GalimAI’s map of company ownership is the truest measure of the policy’s effect.
The public backdrop
| Date | Limited-company BTL landlords | What was happening |
|---|---|---|
| Feb 2016 | 92,975 | Relief begins to be withdrawn from higher-rate taxpayers |
| Mid-2020 | ~200,000 | Section 24 reaches full effect |
| 2024 | 61,517 new companies (+23% on 2023) | New annual record |
| Feb 2025 | 401,744 (+332% since 2016) | ~680,000 properties now company-held |
Hamptons’ analysis of Companies House records puts the public count of buy-to-let companies at 401,744 by February 2025, up 332% from 92,975 in 2016, with a record 61,517 set up in 2024 and roughly three in four new rental purchases now incorporating. That is the public signal; GalimAI’s 463,022-company map is the same shift seen in full, owner by owner.
The most plausible mechanism
The timing and the tax logic line up closely. Section 24 bites only on individually-held, mortgaged portfolios, and incorporation is the single move that fully neutralises it. The curve steepens from exactly the years the restriction phased in, then accelerates again from 2022 as interest rates raised finance costs — and so the size of the deduction individuals could no longer claim. We read this as a strong, well-evidenced correlation with a clear causal channel, not proof that Section 24 alone explains every incorporation: stamp-duty surcharges, succession planning and lender appetite all pushed the same way.
Sources
The proprietary figures in this study (the 463,022 companies, 1,000,000+ owners and the distress signals) are GalimAI first-party data. The public background figures are drawn from:
- Hamptons - record number of companies set up to hold buy-to-let property in 2024
- Section 24 - mortgage interest relief, explained
Frequently asked questions
What is Section 24?
Section 24 of the Finance Act 2015 restricts the tax relief individual landlords get on mortgage interest. Instead of deducting finance costs, they receive a flat 20% tax credit. It was phased in from 2017 and took full effect in April 2020, and it does not apply to property held in a limited company.
What does GalimAI's own data show about it?
GalimAI maps 463,022 property-owning companies and more than 1,000,000 owners across England and Wales - the company-and-SPV market Section 24 made the norm. Each company is linked to its directors, holdings, financing and distress signals, so the boom is visible owner by owner, not just as a public total.
Did Section 24 cause the limited-company boom?
The timing and tax logic line up very closely and incorporation is the clearest way to neutralise Section 24 - a strong, well-evidenced correlation with a clear mechanism. Stamp-duty surcharges, succession planning and lender appetite also contributed, so it is not the only cause.
How can investors use this?
The owners most exposed - higher-rate landlords with geared, individually-held portfolios and over-leveraged SPVs - are a reachable list of named owners in GalimAI, each attached to their property and financing.