“Can you do it for cash?” What cash-in-hand work really costs you.

Is cash in hand illegal?

No. Being paid in cash is not the problem. The problem is income that HMRC never hears about. HMRC calls that the hidden economy: “economic activity that is entirely undeclared to HMRC”^[1].

The duty is to tell HMRC. If your profits from self-employment first make you liable to tax, you must tell HMRC within 6 months of the end of that tax year^[2]. In practice that means registering for Self Assessment by 5 October^[3]. Cash you take and declare is simply turnover.

Why the question comes up

We won't pretend the pressure isn't real. A household paying out of its savings sees your price, not your costs. Someone down the road offers a “cash price”. The van finance is due on the 12th whatever happens.

Wanting to say yes is human. This article is about what saying yes and not declaring it can cost you, and how to get back on the books if you already have. We won't preach. We'll show you the rules and HMRC's own figures, each with a link so you can check it yourself.

How big is the hidden economy in the UK?

HMRC puts the hidden economy at around 6% of the UK tax gap in the 2024 to 2025 tax year^[1]. The whole tax gap, the difference between the tax that should be paid and what is paid, was £59.2 billion, or 6.4% of the tax due^[4].

Small businesses account for the largest share of that gap: 62% in 2024 to 2025^[4]. That is not all cash work: HMRC's tax gap also covers mistakes, failing to take reasonable care, evasion and more^[1].

For income tax, National Insurance and Capital Gains Tax, HMRC estimates the hidden economy tax gap at £1.7 billion in 2024 to 2025, the highest level since the 2005 to 2006 tax year^[5].

Treat these as estimates. HMRC rates its uncertainty as “high” for moonlighters and “very high” for ghosts, and builds the series from a limited number of data points^[5].

The biggest part: side jobs on top of a day job

HMRC splits the hidden economy into two groups^[5]:

• Moonlighters: people who are employees in their main job but do not declare what they earn on the side. Their tax gap was £1.0 billion in 2024 to 2025, the highest level in the series^[5].
• Ghosts: people who declare none of their income to HMRC. Their tax gap was £0.7 billion, also the highest in the series^[5].

So the largest part is not the firm that hides everything. In trade terms it looks like the employed sparky or decorator doing weekend jobs for cash: the day job is taxed through PAYE, the side work is not. If that is you, the side work is self-employment, and the duty to tell HMRC is the same^[2].

What happens if HMRC finds out

If you should have told HMRC about taxable income and didn't, HMRC can charge a failure to notify penalty. It is a percentage of the tax lost because of the failure, which HMRC calls the “potential lost revenue”^[2]. The penalty comes on top of the tax that was due, and HMRC may also charge interest^[2].

How high the percentage goes depends on why it happened^[2]:

• Non-deliberate: up to 30% of the potential lost revenue^[2].
• Deliberate: up to 70%^[2].
• Deliberate and concealed: up to 100%^[2].

For Self Assessment, gov.uk gives a plain example: if you register after 5 October and do not pay all of your tax bill by 31 January, you may get a failure to notify penalty^[6]. If you had a reasonable excuse for a non-deliberate failure, HMRC says it won't charge a penalty^[2].

Telling HMRC before it asks costs less

If you tell HMRC about the failure before you have any reason to think it is about to find out, HMRC calls it an “unprompted disclosure”. Any other time it is “prompted”^[2]. The minimum penalty is lower for an unprompted disclosure^[2]. HMRC's ranges are:

• Non-deliberate, unprompted, within 12 months of the tax being due: 0% to 30%^[2].
• Non-deliberate, unprompted, 12 months or more after: 10% to 30%^[2].
• Non-deliberate, prompted: 10% to 30% within 12 months, 20% to 30% after that^[2].
• Deliberate: 20% to 70% unprompted, 35% to 70% prompted^[2].
• Deliberate and concealed: 30% to 100% unprompted, 50% to 100% prompted^[2].

Where you land within the range depends on how much you help: telling HMRC, helping it work out the figures and giving access to your records each reduce the penalty^[2]. We won't work out a figure for you. Your accountant can, on your real numbers.

What your customer loses

A homeowner who pays you cash still has rights. Under the Consumer Rights Act 2015 every contract to supply a service includes a term that you will do it with reasonable care and skill^[7]. What you tell them about the job or yourself, in words or in writing, can become binding^[8]. If the work isn't up to that, they can make you redo it at your own cost^[9], or claim a price reduction, refunded within 14 days of you agreeing to it^[10]. A trader cannot sign those rights away^[11].

Those rights don't vanish without paperwork, but a written quote and an invoice are how both of you prove what was agreed and what was paid. Without them, a dispute is your word against theirs.

What it costs you, beyond a penalty

The penalty is the obvious risk. These are the quieter ones:

• Work for contractors: a main contractor has to pay you under the Construction Industry Scheme. Registered, they deduct 20% for HMRC; not registered, they must take 30%^[12]. Registered deductions count as advance payments towards your tax and National Insurance bill^[12].
• Gross payment status: since 6 April 2026 HMRC can remove it immediately from a business that knew or should have known its payments were linked to tax fraud, charge a penalty of up to 30% of the lost tax, and bar it from reapplying for 5 years^[13].
• A business you can't show: jobs that aren't on paper don't appear in your accounts, so they won't help you when a lender, a buyer or a business customer asks to see them.
• No records to fall back on: a sole trader must keep records for at least 5 years after the 31 January deadline^[14]. Cash jobs leave nothing behind when HMRC or a customer asks.

Myths and facts

A few things you hear on site, and what the rules and HMRC's figures say.

Myth: “Getting paid in cash is illegal.”

Fact: No. The duty is to declare the income. HMRC's term for the problem is the hidden economy: activity “entirely undeclared to HMRC”^[1].

Myth: “A few weekend jobs on the side don't count.”

Fact: They are exactly what HMRC measures. Undeclared side income from people with a day job, the moonlighters, is the largest part of the hidden economy tax gap: £1.0 billion in 2024 to 2025^[5].

Myth: “If HMRC catches you, it's double the tax straight away.”

Fact: The penalty depends on behaviour and on whether you told HMRC first. For a non-deliberate failure disclosed unprompted within 12 months, the range starts at 0%^[2].

Myth: “A customer who pays cash has no comeback.”

Fact: The Consumer Rights Act applies to every contract to supply a service^[7]. Without a quote and an invoice, it is just harder for either side to prove what was agreed.

The honest route back

This is not advice from an accountant. It is a list of where to start and where to check:

• Price properly: work out the rate you need with the hourly rate calculator, then see what your last quote really paid per hour with the quote check.
• Take deposits: ask for a deposit before you buy materials, so a customer's savings pay for their job, not yours.
• Register: if you're not registered for Self Assessment, the deadline is 5 October after the end of the tax year^[3].
• Tell HMRC about the past: an unprompted disclosure has a lower minimum penalty than one HMRC prompts^[2]. HMRC's factsheet CC/FS11 explains how it works out the penalty^[2].
• Work for contractors: register for CIS, so deductions are 20% rather than 30%^[12].
• Get an accountant: let them work out your figures before you file anything.
• Your own list: the duties and rights check shows what applies to you on tax, CIS, staff and customer contracts.

How to win the job without a “cash price”

A customer who can afford to pay properly wants to be sure they won't get a cowboy. You win them with what a cowboy doesn't have:

• A quote on the visit: clear, itemised, with photos, before you leave the house.
• Photos of finished jobs you can show on your phone.
• A quick reply, while they're still deciding.
• Everything on paper: the quote, the changes they approved and the invoice. For someone spending their own savings, that is peace of mind.

Sources

Every figure in this article has the number of its source in square brackets. We last checked every link on 24 October 2026. Figures are given exactly as the source states them.

1. [1]Measuring tax gaps 2026 edition: 7. Illustrative tax gap by behaviour. HM Revenue & Customs, 2026.
2. [2]Compliance checks: penalties for failure to notify (CC/FS11). HM Revenue & Customs, 2026.
3. [3]Self Assessment tax returns: deadlines. GOV.UK, 2026.
4. [4]Measuring tax gaps 2026 edition: 1. Tax gaps summary. HM Revenue & Customs, 2026.
5. [5]Measuring tax gaps 2026 edition: 4. Income Tax, National Insurance contributions and Capital Gains Tax. HM Revenue & Customs, 2026.
6. [6]Self Assessment tax returns: penalties. GOV.UK, 2026.
7. [7]Consumer Rights Act 2015, section 49 (service to be performed with reasonable care and skill). legislation.gov.uk, 2015.
8. [8]Consumer Rights Act 2015, section 50 (information about the trader or service to be binding). legislation.gov.uk, 2015.
9. [9]Consumer Rights Act 2015, section 55 (right to repeat performance). legislation.gov.uk, 2015.
10. [10]Consumer Rights Act 2015, section 56 (right to price reduction). legislation.gov.uk, 2015.
11. [11]Consumer Rights Act 2015, section 57 (liability that cannot be excluded or restricted). legislation.gov.uk, 2015.
12. [12]What you must do as a Construction Industry Scheme (CIS) subcontractor. GOV.UK, 2026.
13. [13]Tackling Construction Industry Scheme fraud. HM Revenue & Customs, 2025.
14. [14]Business records if you're self-employed: how long to keep your records. GOV.UK, 2026.