Associated Companies and Marginal Relief: The Corporation Tax Trap for Multi-SPV Investors

Most property investors set up a second or third SPV without giving corporation tax rates a second thought — each company is a separate legal entity, so surely each gets its own slice of the 19% small profits rate. It doesn't work that way. The associated companies rule shares those thresholds across every company under common control, and for an investor running several SPVs, that can mean paying the higher rate on profits that would otherwise sit comfortably in the lower band.

Why this exists

Since April 2023, Corporation Tax has had two headline rates either side of a marginal band: 19% on profits up to £50,000 (the small profits rate), 25% above £250,000 (the main rate), with marginal relief tapering the effective rate in between. Those thresholds were set on the assumption of one company, one set of profits. Without a further rule, a group could simply split one profitable trade across several small companies, keeping every one of them under £50,000 and paying 19% on the lot. The associated companies rule closes that gap by dividing the £50,000 and £250,000 thresholds by the total number of associated companies, including the one doing the calculation.

The test: control, not just ownership

Two companies are associated if one controls the other, or both are under the control of the same person (or the same group of people acting together) at any point during the accounting period — even for a single day. Control generally means holding more than 50% of the ordinary share capital, the voting rights, or the rights to assets on a winding-up. For a sole director-shareholder running several personal SPVs, every one of those companies is associated with every other one, because the same person controls each.

It gets wider still. Where there is substantial commercial interdependence between two companies — shared premises, shared finance or funding arrangements, one trading mainly with the other, or common customers and suppliers — the rights held by an individual's associates (spouse, civil partner, and minor children, among others) can be attributed back to that individual for the purposes of the test. Splitting shareholdings across a couple running property companies together does not, on its own, get around the rule if the businesses remain commercially entwined.

Where property investors get caught out

The structure that causes the most surprise is the one this firm sees most often: a director running one SPV per development or per handful of buy-to-lets, each opened with the same, sensible ring-fencing logic covered in our guide to when an SPV makes sense. Ring-fencing liability and simplifying lender security are good reasons to use separate companies. What often isn't factored in is that every one of those companies is associated the moment they share a controlling shareholder, regardless of whether they ever transact with each other, share a bank account, or even share a registered address.

A second version of the same trap: an SPV that has finished its project and is sitting dormant, or one bought off the shelf and not yet trading. Genuinely dormant companies — with no significant accounting transactions in the period — are excluded from the count. A company that is simply holding an asset, waiting for its first deal, or ticking over with minimal activity is not dormant in the relevant sense, and still counts.

Worked example

Take an investor with three wholly owned SPVs, each making £40,000 of taxable profit in the year. Considered alone, £40,000 sits comfortably under the £50,000 small profits threshold, so each company might expect to pay 19%. Because all three are associated, each company's own thresholds are divided by three: the lower limit becomes £16,667 and the upper limit £83,333. Every one of the three companies is now above its own lower limit, so instead of 19% flat, each pays tax within the marginal relief band — an effective rate above 19% and climbing towards 25% as profit rises towards the reduced upper limit. Add a fourth associated company and the lower limit falls to £12,500; a £40,000 profit in each company now sits well into marginal relief, and a company earning close to £50,000 crosses into paying close to the full 25% main rate on a chunk of what looked like small-company profit.

It applies per company, cumulatively, not just once

A common misreading is to assume the rule only bites once total group profits exceed £50,000. It doesn't. The division happens to each associated company's own thresholds individually, based purely on the count of associates — it takes no account of how profitable the other companies actually are. Two SPVs, one profitable and one loss-making or barely trading, still halve each other's thresholds. There is no netting-off and no exemption for a company that happens to be small in absolute terms if it is associated with others.

What you can actually do about it

The associated companies rule is a structural fact, not something to be planned around with clever paperwork — HMRC's attribution rules exist precisely to catch attempts to disguise common control. What is worth doing is making sure the rule is factored into decisions you do control:

• Model the real effective rate before assuming a new SPV keeps you at 19%. The number of existing associated companies changes the answer for every company in the group, not just the new one.
• Align accounting periods where practical, so the associated companies count and the marginal relief calculation are easier to track and forecast consistently year to year.
• Wind up genuinely spent companies rather than leaving a finished-project SPV sitting on the register with minor residual activity — see our guide to extracting profit from a property company for how a Members' Voluntary Liquidation fits into that decision.
• Weigh a holding company structure against a flat set of siblings; it does not remove the association, but it can simplify group relief, loss relief and cash movement between companies that are associated in any case — the trade-offs are similar to those covered in our note on Family Investment Companies for property portfolios.
• Get the profit split right at the outset when structuring a joint venture, since co-controlled companies with unrelated other shareholders may or may not be associated depending on how control is actually held — a question worth resolving before signing, as discussed in our guide to JV structures for property development.

Common mistakes

• Assuming each SPV gets its own untouched £50,000 band because it is a separate legal entity
• Treating a quiet, non-trading SPV as automatically excluded without checking whether it meets the dormancy test
• Splitting shareholdings among family members without addressing the underlying commercial interdependence between the companies
• Forgetting that the count includes companies associated for only part of the accounting period, not just those associated throughout
• Not revisiting the group's effective rate each time a new SPV is incorporated or an old one is wound up

Why it is worth getting right

None of this changes the case for using SPVs where ring-fencing, financing or exit reasons justify it. What it changes is the tax modelling that sits behind the decision. An investor comparing one large SPV against several smaller ones needs to run the corporation tax numbers on the associated basis from day one, not discover at filing time that a structure assumed to be paying 19% across the board has quietly been paying an effective rate several points higher on every company in the group.

Common questions

What counts as an associated company for corporation tax?

A company is associated with another if one controls the other, or both are under the control of the same person or group of persons, at any point in the accounting period. Control means more than 50% of the shares, voting rights, or the rights to assets on a winding-up, and the rights of certain associates — such as a spouse, civil partner, or minor children — can be attributed to you where there is substantial commercial interdependence between the companies.

Does an associated company have to be trading to count?

No. Dormant companies with no significant accounting transactions in the period are excluded, but a company that is simply holding an asset, sitting between projects, or not yet trading still counts as associated if it is under common control. Passive holding companies and shell SPVs waiting for their first deal are a common trap.

How many SPVs can I run before it affects my tax rate?

There is no safe number — the thresholds simply divide by the total count of associated companies from the first one. Two commonly owned SPVs already halve both the £25,000 lower limit and the £125,000 upper limit that apply to each company; a fourth SPV takes the lower limit down to £5,000.

Can I avoid the associated companies rule by using different family members as shareholders?

Rarely, and it is not a planning technique worth relying on. HMRC attributes associates' rights back to you specifically to catch this kind of arrangement wherever there is substantial commercial interdependence — shared premises, shared finance, shared customers or suppliers, or one company depending on the other. Spreading shares around the family without genuinely separating the underlying businesses does not remove the association.

This article is general information, not personal tax advice, and tax rules change. Your own position depends on facts we cannot see from here — please take advice before acting on anything above.

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