Stamp duty penalties and the reasonable care defence (2026)

When HM Revenue & Customs overturns a stamp duty claim and reclaims the tax, the headline figure that follows is usually the penalty. On a reclassified "non-residential" purchase, that penalty can reach the full amount of the underpaid tax — up to £30,500 on the worked example below. Yet the same rules that set the penalty also switch it off entirely in one circumstance: where the original error was made with reasonable care.

This is the part of the penalty regime that gets the least attention. A stamp duty error made honestly, with reasonable care, still leaves the buyer owing the reclaimed tax and interest — but it carries no penalty at all. Understanding where that line sits, and how far a buyer can lean on a professional adviser to stay on the right side of it, is the difference between a bill and a much larger bill.

This is general information about how the rules work, not advice. Speak to a qualified adviser before acting.

Where the penalty comes from

When a Stamp Duty Land Tax (SDLT) return understates the tax due — for example, by treating a house as "non-residential" or "uninhabitable" and paying the lower commercial-scale rates — HMRC can open an enquiry, issue a discovery assessment to reclaim the difference, add interest, and charge a penalty for the inaccuracy. The full mechanics of that three-layer exposure are set out in our guide to failed non-residential SDLT claims and the discovery-assessment process.

The penalty itself sits under Schedule 24 of the Finance Act 2007. Crucially, it is charged as a percentage of the potential lost revenue (PLR) — the tax that was underpaid — and the percentage depends entirely on the taxpayer's behaviour, not on the size of the error.

To ground the numbers: a £400,000 additional-property purchase carries SDLT of £30,000 on the standard residential scale with the 5% surcharge, versus £9,500 on the non-residential scale (figures from the Homecost stamp duty calculator and the HMRC commercial scale, fetched 23 July 2026). If a "non-residential" claim on that purchase is overturned, the PLR is the £20,500 gap. At £600,000 the gap widens to £30,500. The full ladder:

The surcharge is what makes the reclaim costly — the standard-versus-non-residential gap for an owner-occupier is a flat £500 band artefact, as covered in where the derelict-versus-doer-upper line falls. It is buyers of second homes and buy-to-lets, escaping the surcharge, who stand to lose the most if a claim fails.

Reasonable care switches the penalty off

Schedule 24 does not penalise every inaccuracy. Paragraph 3 sorts inaccuracies into categories: an error is "careless" if it was due to a failure to take reasonable care, and "deliberate" if the taxpayer knew the document was wrong. Only careless and deliberate inaccuracies attract a penalty. An inaccuracy made despite reasonable care — an honest mistake by a diligent taxpayer — falls outside the penalty entirely.

The practical effect is stark. Applying the standard Schedule 24 percentages to the £30,500 PLR at £600,000:

The tax and the interest survive in every row — reasonable care is not a defence to the reclaimed tax itself. But the penalty column collapses to zero. That is why the behaviour question, not the size of the error, tends to be the real battleground once HMRC challenges a claim.

What "reasonable care" actually means

The legislation does not define reasonable care with a checklist. The leading tribunal statement, in David Collis v HMRC (2011), is that reasonable care is judged by the standard of a prudent and reasonable taxpayer in the position of the taxpayer in question. HMRC's own Compliance Handbook echoes this: what is reasonable depends on the person's abilities and circumstances, and a taxpayer is expected to take more care over larger or more complex transactions.

Importantly, HMRC accepts that a taxpayer is not expected to have the specialist knowledge of a tax professional. The bar is diligence, not expertise. Where a point is genuinely uncertain, telling HMRC about it — rather than quietly taking the favourable position — is one of the clearest markers of care.

How far you can rely on an adviser

Most buyers do not file their own SDLT return; a conveyancer or a specialist firm does. Schedule 24 anticipates this. Paragraph 18 — the agency rule — makes a taxpayer responsible for inaccuracies in documents filed on their behalf, but provides that the taxpayer is not liable to a penalty for something done by their agent where the taxpayer took reasonable care to avoid the inaccuracy.

Reliance on a competent professional can therefore discharge the reasonable-care duty. In Hanson v HMRC (2012), a taxpayer who relied on his accountant was found to have taken reasonable care, and the penalty was cancelled; the decision was upheld on appeal. But the shield is conditional. Two things have to hold:

1. You gave the adviser the full and correct facts. An adviser who is under-instructed — not told, say, that the "derelict" property had a functioning kitchen and was let shortly after purchase — cannot immunise a claim built on the missing facts.
2. You did not ignore an obvious error. The taxpayer must still apply the checking a prudent lay person reasonably could. Relying on advice that was plainly too good to be true, without question, is not reasonable care.

Put simply, the reliance defence protects a buyer who engaged a competent adviser honestly and completely. It does not protect a buyer who steered the adviser toward a favourable answer, or who signed off on a claim they had reason to doubt.

Why this matters for the reclaim market

A "no win, no fee" industry has grown up around reclaiming SDLT on run-down homes, encouraging buyers to argue that a property was "uninhabitable" and therefore non-residential. The prize is real — escaping the surcharge is worth £13,000 to £30,500 across the examples above — but the pool of genuinely qualifying property is small. Homes changing hands at or below £50,000, a rough proxy for genuinely derelict, non-dwelling stock, made up just 0.30% of England & Wales residential sales in 2025 (2,291 of 763,112 transactions; HM Land Registry Price Paid Data, fetched 23 July 2026). The reclaim marketing is far larger than the sliver of stock that actually clears the legal bar, which is set high — see the derelict-versus-doer-upper boundary test.

Where a reclaim is overturned, the reasonable-care question decides whether a penalty lands on top of the reclaimed tax and interest. A buyer who signed an aggressive claim on a promoter's say-so, without giving the full facts or checking an obviously optimistic position, may struggle to reach the paragraph 18 shield — because the reasonable-care standard looks at what they did, not only at what the promoter said. HMRC also carries the burden of showing that an error was careless or deliberate before any penalty applies, a point we cover in the carelessness and deliberate evidence bar, and the meaning of "deliberate" was tightened by the Supreme Court in the case discussed in our Tooth discovery-assessment explainer.

The takeaway

Reasonable care is a complete defence to the Schedule 24 penalty, though never to the reclaimed tax or the interest. It turns on the taxpayer's own diligence: giving a competent adviser the full facts, checking advice a prudent person would question, and disclosing genuine uncertainty rather than banking the favourable reading. To see how the underlying figures move across the surcharge thresholds, try the Homecost stamp duty calculator, and to gauge the price bands where reclaim marketing tends to cluster, look up renovation-heavy areas such as Bradford in the Homecost tool. You can browse the rest of our cost-intelligence guides for the wider SDLT picture, including the additional-property surcharge that sits behind most reclaim disputes.

This is general information about how the penalty rules work, based on published statute, HMRC guidance and tribunal decisions. It is not tax or legal advice, and it does not value any individual property. Speak to a qualified adviser before acting.