HMRC Shield is the only pre‑submission protection layer built specifically for UK sole traders and small businesses. It catches errors before they reach HMRC — so you never have to explain yourself after the fact.
Around 1 million people missed the Self Assessment deadline in January 2026 — and they all faced an immediate penalty the moment they did.
Miss your filing deadline by one day: £100 automatic penalty. Three months late: up to £1,000. Twelve months late: at least £1,600. None of this requires you to have done anything dishonest — just late.
1 day late — £100 automatic, regardless of tax owed.
3 months late — additional £10/day up to £900.
6 months late — £300 or 5% of tax due (whichever is greater).
12 months late — another £300 or 5% of tax due.
Maximum potential — £1,600+ before interest charges.
Late payment interest — 8.00% per annum.
MTD points system — repeated late quarterly submissions trigger £200 penalties once you hit the points threshold.
Most tax software checks whether your filing is in the correct format before submitting it. Shield goes further. It checks whether what you're claiming is actually allowable — before a single number reaches HMRC.
There are two kinds of filing mistakes. Format errors — missing fields, wrong dates, invalid structure. Basic software catches those. Substance errors are different: a personal expense claimed as business, a gym membership filed as professional development, a client lunch treated as an allowable deduction when it isn't. Those are the errors that get people investigated. Shield catches those.
Every transaction is checked against HMRC SA103 allowable expense rules.
Potentially non‑compliant deductions are flagged before submission.
Duplicates, inconsistent categorisation, and audit‑risk patterns are detected automatically.
• Entertainment expenses (never allowable for sole traders).
• Gym memberships and other personal fitness costs.
• Personal streaming subscriptions (Netflix, Spotify, Disney+, Amazon Prime).
• High‑value claims with no receipt or justification attached.
• Duplicate transactions from the same merchant in a short window.
• The same merchant categorised differently in different months.
• Income approaching the £90,000 VAT registration threshold.
• Personal Allowance tapering warnings for income near £100,000.
• Capital purchases miscategorised as running costs.