Running a small business in Harrow, Wembley, or Stanmore is hard enough without HMRC catching you out on avoidable mistakes. As a local HMRC-registered accountant based in Stanmore, I see the same errors come up time and again.

Here are the five most costly ones — and how to fix them.

1. Missing the Self-Assessment Deadline

The 31 January deadline catches out hundreds of local business owners every year. Even if you have no tax to pay, filing late triggers an automatic £100 fine — and that climbs fast if you keep delaying. If you’re a sole trader, company director, or landlord, you almost certainly need to file a return.

Fix it: Get organised early. I can have your return filed within days of receiving your records.

2. Not Claiming All Allowable Expenses

Too many small business owners in Harrow leave money on the table by not claiming everything they’re entitled to. Home office costs, mileage, professional subscriptions, phone bills — if it’s wholly and exclusively for business, it’s likely deductible.

Fix it: Keep your receipts and let a qualified accountant review your expenses before you file. A few hours of professional review typically saves far more than it costs.

3. Getting VAT Wrong

If your turnover is approaching £90,000 (the current VAT registration threshold), you need to be monitoring this closely. Crossing the threshold without registering — or registering incorrectly — creates penalties and interest. Equally, many businesses register voluntarily and then fail to file VAT returns on time.

Fix it: I handle VAT registration, preparation, and submission for local businesses across Harrow, Stanmore, and Edgware.

4. Mixing Personal and Business Finances

This is especially common with sole traders. Using the same bank account for personal and business spending makes your bookkeeping a mess and increases the risk of errors on your tax return — errors that could trigger an HMRC investigation.

Fix it: Open a dedicated business bank account. It costs nothing and makes everything cleaner.

5. Not Accounting for the 2025/26 Tax Year Changes

The tax landscape changes every April, and many small business owners aren’t aware of the adjustments to National Insurance, dividend allowances, and Corporation Tax reliefs that have come into effect. Filing based on outdated information can mean either overpaying or underpaying — both are problems.

Fix it: Work with an accountant who stays current. I’m an HMRC-registered agent and keep my clients updated on anything that affects them.

Ready to sort out your taxes? I’m Talha Alvi, Director of Your Tax Help Accountants — based in Stanmore and serving small businesses across Harrow, Wembley, and Edgware. Fixed monthly fees. No jargon. Email me at info@yourtaxhelp.co.uk.