SDLT linked transactions are property deals that HMRC treats as a single purchase for tax purposes, adding the prices together and charging Stamp Duty Land Tax on the combined figure rather than on each deal in isolation. The rule sits in Section 108 of the Finance Act 2003 and applies to property in England and Northern Ireland. Scotland and Wales run separate land transaction taxes with their own aggregation rules, so nothing below applies to purchases there. The practical effect is almost always more tax: aggregation tends to push each purchase into a higher band, and a later linked deal can force you to top up the tax you already paid on an earlier one.
When Two Deals Count as Linked
Section 108 treats transactions as linked when they form part of a single scheme, arrangement, or series of transactions between the same buyer and seller, or between persons connected with either of them.
In practice, HMRC looks at the commercial reality. A single arrangement exists when several properties are bought under one contract or through interdependent negotiations. A series covers sequential purchases where the intent to buy multiple units existed from the start. Months between completion dates does not break the link if the deals were contemplated together from the outset.
The factors that matter are whether one purchase was conditional on another, whether the same negotiation produced all the deals, and whether a shared commercial purpose ties them together. If you want two purchases treated separately, you need clear evidence that each stands on its own, with no overarching plan connecting them. Where two or more linked transactions share the same effective date, the buyers can file a single return covering all of them as one notifiable transaction.
Who Counts as a Connected Person
Because linking catches deals between the same parties “or persons connected with them,” the connected persons definition does a lot of the work. Section 108 borrows the definition from Section 1122 of the Corporation Tax Act 2010, and it casts a wide net.
You are connected to your spouse or civil partner, your siblings, and your direct ancestors and descendants (parents, grandparents, children, grandchildren). You are also connected to the spouses and civil partners of those relatives, and to the siblings, ancestors, and descendants of your own spouse or civil partner. Business partners count, as do their spouses, civil partners, and relatives on the same definition. Companies you control alone or together with connected persons are connected to you, and two companies are connected if the same person or group controls both. Trustees of a settlement are connected to the settlor and to anyone connected with a living settlor.
One point worth pinning down: “relative” here means brother, sister, ancestor, or lineal descendant only. Nieces, nephews, uncles, and aunts fall outside. A purchase by an uncle and a separate purchase by a niece from the same seller will not be linked on family grounds alone.
How the Tax Is Calculated on the Aggregate
The calculation runs in two steps. Add the total consideration for every linked transaction, work out SDLT on that combined figure at the standard rates, then apportion the resulting tax to each individual deal based on its share of the total price.
From April 2025, the standard residential rates are 0% up to £125,000, 2% on the slice from £125,001 to £250,000, 5% from £250,001 to £925,000, 10% from £925,001 to £1.5 million, and 12% above £1.5 million. Buyers who already own a residential property pay a 5% surcharge on top of these rates when acquiring an additional dwelling. Non-UK residents pay a further 2%.
A Worked Example of the Cascade
Say you buy three houses from the same builder: the first for £280,000 as your home, then a second and third for £275,000 each as investments, all linked as part of a series.
On the first purchase, you pay tax on £280,000 alone: 0% on £125,000, 2% on the next £125,000, and 5% on the last £30,000, totalling £4,000.
When the second house completes, the aggregate becomes £555,000. You recalculate tax on the full £555,000 at standard rates, giving £17,750. The first house’s share is £17,750 × (£280,000 ÷ £555,000) = £8,954. You have already paid £4,000, so you owe another £4,954 on that first transaction. The second house also attracts the 5% higher rates surcharge because you now own more than one property. Tax on the whole £555,000 at higher rates comes to £45,500, and the second house’s share is £45,500 × (£275,000 ÷ £555,000) = £22,545. Both amounts fall due at the same time.
The third purchase repeats the exercise with a new aggregate of £830,000, triggering another recalculation and further top-ups on the earlier returns. This is what catches buyers off guard: each new linked deal can raise the tax owed on every previous one.
The Six or More Dwellings Rule
If you buy six or more residential properties in a single transaction, or as part of linked transactions, HMRC treats the entire purchase as non-residential. The non-residential rates are 0% up to £150,000, 2% from £150,001 to £250,000, and 5% above £250,000, which sit well below the top residential bands.
This treatment has applied since 1 June 2024 and replaced Multiple Dwellings Relief, which had let buyers average the price across units and apply residential rates to the average. MDR was abolished for transactions completing on or after 1 June 2024, with limited transitional protection for contracts exchanged on or before 6 March 2024. For anyone acquiring six or more homes together, the shift to non-residential rates is now the main route to a lower bill on a bulk residential purchase.
Mixed-Use and Non-Residential Linked Deals
Where linked transactions include both residential and non-residential elements, the whole group is assessed at the non-residential and mixed-use rates. A flat above a shop is the standard example. The non-residential rates top out at 5% above £250,000, against 12% for high-value residential purchases, so mixed-use classification can cut the bill sharply.
The 5% higher rates surcharge for additional dwellings does not apply to non-residential or mixed-use transactions, and neither does the 2% non-UK resident surcharge. HMRC can challenge a mixed-use claim if the non-residential element is trivial or artificial, so classification needs to be right at the outset rather than assumed.
Reporting a Linked Transaction
On form SDLT1 you tick “Yes” at question 13 (or the equivalent field online) to flag the transaction as linked, then enter the total consideration for all linked transactions, not just the price of the property you are currently reporting. The return also asks for the Unique Transaction Reference Number of any previously submitted linked returns.
HMRC’s penalty regime for inaccurate returns runs from 0% for careless errors that the taxpayer discloses voluntarily up to 100% of the tax due for deliberate and concealed inaccuracies that HMRC finds on its own. Under-declaring the aggregate figure is where those penalties usually start.
Amending Earlier Returns After a Later Linked Deal
When a later linked transaction increases the aggregate and pushes earlier deals into higher rate bands, the earlier returns need revisiting. What you do depends on the status of the original transaction.
If the original return was filed and tax was paid, you submit a further return for that original transaction, typically as a letter to the Stamp Office quoting the original UTRN, giving the new transaction details, and self-assessing the additional tax. Payment is due within 30 days of the later linked transaction. If the original return was filed but no tax was due at the time, the same process applies: write in with the original UTRN, recalculate, and pay within 30 days.
If the original transaction was not previously notifiable and the later linked deal pushes it above the notification threshold for the first time, you now have to file an SDLT1 for that original transaction. Since 1 March 2019, the deadline is 14 days from the later linked transaction. Missing any of these deadlines adds late filing penalties on top of the additional tax and interest.
Trying to Avoid Linking: Section 75A
Section 75A of the Finance Act 2003 is HMRC’s broad anti-avoidance tool for property. It bites whenever a series of transactions produces less SDLT than a straightforward direct transfer between the same parties would have done. The Supreme Court confirmed in Project Blue Ltd v HMRC [2018] that this is a purely objective test: HMRC does not have to prove a tax avoidance motive. If the arithmetic shows a saving from routing the deal through multiple steps instead of one, the section can apply.
When it applies, HMRC disregards the individual steps and substitutes a notional direct transfer from the original seller to the ultimate buyer. Tax is charged on the largest amount paid by any one person across all the steps, or the largest amount received by the seller or anyone connected with the seller. Section 75A runs alongside Section 108 rather than as an alternative: genuinely linked deals are aggregated under Section 108, and Section 75A is there for arrangements structured specifically to fall outside the linked transaction definition while achieving what is really a single acquisition.