How the UK Tax System Works
HMRC collected over £800 billion in the 2023/24 tax year. Income tax, National Insurance, VAT, corporation tax, capital gains tax, inheritance tax — the list is long and the details shift with each Budget. Most people only need to engage with a small slice of this machine, but getting that slice right matters.
The tax year runs from 6 April to 5 April, an oddity that dates back to 1752 when Britain switched from the Julian to the Gregorian calendar and the Treasury did not want to lose 11 days of revenue. The deadlines are fixed: paper tax returns by 31 October, online returns by 31 January, and payment also by 31 January. Late filing attracts an automatic £100 penalty even if no tax is owed. After three months, daily penalties of £10 start accumulating, up to a maximum of £900, plus further penalties at six and twelve months.
Self Assessment: Who Needs to File
You must submit a Self Assessment tax return if you are self-employed and earned more than £1,000 in the tax year, a partner in a business partnership, a company director (unless it is a non-profit organisation and you are unpaid), or if you have untaxed income such as rental income, tips, investment income, or foreign income. The £1,000 threshold for trading income is the trading allowance — below that, you do not need to register. Above it, you do.
The Self Assessment registration process is straightforward but takes time: HMRC sends your Unique Taxpayer Reference (UTR) by post and the letter can take 10 working days. Add another week to activate your online account. If you leave this until January, you are gambling with the deadline. Register in April or May and give yourself a full year to prepare.
The online Self Assessment portal guides you through the return section by section. It calculates the tax as you go. The system is not pretty but it works. If your affairs are complex — multiple income streams, capital gains, foreign income — you may need an accountant. A good one saves more in tax than they charge in fees. The professional bodies to check are the ICAEW, ACCA, and AAT for qualified practitioners.
Income Tax and National Insurance
The personal allowance — the amount you can earn before paying income tax — is £12,570 for 2024/25. It starts to reduce once your income exceeds £100,000, disappearing entirely at £125,140. Effectively, this creates a 60% marginal tax rate in that band, which catches out high earners who do not plan for it. Pension contributions are the main way to bring income back below the threshold.
Income tax bands for 2024/25: the basic rate is 20% on income from £12,571 to £50,270. The higher rate is 40% from £50,271 to £125,140. The additional rate is 45% above £125,140. Scotland has different bands.
National Insurance for employees is 8% on earnings between £12,570 and £50,270, and 2% above that. For the self-employed, Class 2 NI is £3.45 per week if profits exceed £6,725; Class 4 NI is 6% on profits between £12,570 and £50,270 and 2% above that. Class 2 was supposed to be abolished in 2024 but the government backtracked — for now, it remains in place for the self-employed.
VAT, Corporation Tax, and Business Taxes
VAT registration becomes mandatory when your taxable turnover in any rolling 12-month period exceeds £90,000. You can register voluntarily below that if it benefits your business — for example, if most of your customers are VAT-registered and can reclaim the VAT you charge. Once registered, you must charge VAT at the standard rate of 20% (with reduced rates of 5% and 0% for certain goods and services), file quarterly returns through Making Tax Digital, and keep digital records.
Making Tax Digital (MTD) is the government’s long-running project to move all tax reporting online. MTD for VAT has been mandatory since April 2022 for all VAT-registered businesses, regardless of turnover. MTD for Income Tax Self Assessment is being phased in from April 2026 for taxpayers with income above £50,000 and from April 2027 for those above £30,000. When it arrives, quarterly updates through compatible software replace the annual return.
Corporation tax applies to limited companies on their profits. The main rate is 25% for profits over £250,000, with a small profits rate of 19% for profits up to £50,000, and marginal relief between the two. The return is due 12 months after the accounting period ends, but payment is due nine months and one day after. This lag means you need to keep money aside — a company can look profitable and still run out of cash if the tax has not been reserved.
Common Mistakes and How to Fix Them
The most frequent Self Assessment error is claiming expenses you are not entitled to. The rule is that expenses must be wholly and exclusively for business purposes. A mobile phone contract in your name where you also make personal calls: HMRC will disallow it unless you can show a clear split. The simpler test is: would you have spent this money if you were not running the business? If the answer is no, it is probably allowable.
Another common problem is paying the wrong amount because of payments on account. Self Assessment demands two payments on account each year — 31 January and 31 July — each equal to half of your previous year’s bill. These go toward your next year’s liability. Many first-time filers do not realise this and are hit with a January bill that is 150% of what they expected: their full current-year tax plus 50% toward next year.
If you cannot pay, contact HMRC before the deadline. They are more reasonable than people expect and will agree to a Time to Pay arrangement. You pay interest (currently 7.75%), but you avoid the 5% late payment surcharge at 30 days, and the further 5% at six months and twelve months. Silence is the expensive option.
Official Resources
The HMRC website houses every piece of guidance you will need. The income tax calculator gives a take-home pay estimate. The Self Assessment ready reckoner estimates your tax bill before you file. The Low Incomes Tax Reform Group (LITRG) publishes clear guides for people on low incomes. The Chartered Institute of Taxation maintains a directory of qualified tax advisers if your situation calls for professional help.
Official Contacts
UK: HMRC Income Tax Helpline — 0300 200 3300. https://www.gov.uk/hmrc
India: Income Tax e-Filing — https://www.incometax.gov.in. Helpline — 1800 103 0025
Email: HMRC: use your online account or the contact form. India IT Dept: helpdesk@incometax.gov.in