Is Contractor Arbitrage Legal in the UK?

Contractor arbitrage is legal in the UK. Winning the job as the main contractor, subcontracting the physical work to specialist trades, and keeping the margin between the two prices is how UK construction has always worked. The model is fine; the compliance you cannot skip is HMRC's Construction Industry Scheme.

I run this model. The short answer is there is no law in England, Wales, Scotland or Northern Ireland that bans acting as the main contractor and subcontracting the work. Every major housebuilder, every housing association maintenance contract, every commercial fit-out firm does exactly this. Here is the compliance picture in full.

Why contractor arbitrage is legal in the UK#

Contractor arbitrage is the business model where you enter the prime contract with the client, subcontract delivery to vetted specialist trades, and keep the spread between what the client pays and what the work costs. You carry the contract, the responsibility and the client relationship. Your subcontractors carry the tools.

That sits squarely within a well-established legal category: main contracting. UK law recognises it, regulates it, and has specific compliance obligations for it. The obligation is not a special licence - it is primarily CIS, and then VAT once you are large enough.

Do you need a contractor licence for contractor arbitrage in the UK?#

This is where the UK differs significantly from the US and Australia, and it surprises people coming from those markets.

England, Wales, Scotland and Northern Ireland have no mandatory general contractor licence for private construction work. Unlike California's CSLB or New South Wales Fair Trading, there is no national licensing board you must pass through before entering a prime contract on a private job.

The UK has voluntary schemes - TrustMark and the Construction Skills Certification Scheme (CSCS) - and some commercial clients ask for them, but they are not a legal requirement to act as the prime contractor.

Where licensing does apply:

• Regulated specialist work: Electrical work notifiable under Part P of the Building Regulations requires a registered electrician. Gas work requires a Gas Safe registered engineer. These requirements apply to your subcontractors, not to you as the prime.
• Higher-risk buildings: Under the Building Safety Act 2022, if you act as principal contractor on a building 18 metres or taller, or 7 or more storeys, you must register with the Building Safety Regulator at HSE and meet mandatory competence requirements.
• Asbestos: Any work disturbing asbestos requires an HSE licence held by your sub.
• Licensing consultation: A government call for evidence on licensing and registration for built environment professions and trades ran from 20 May to 12 August 2026. Nothing has been legislated as of today.

For standard private construction and property maintenance - where most contractor arbitrage operators start - no general contractor licence is required. The compliance that matters is what follows.

CIS - the one compliance requirement you cannot skip#

The Construction Industry Scheme (CIS), run by HMRC, is the most significant compliance requirement that distinguishes UK contractor arbitrage from the US or Australian version. If you pay subcontractors for construction work, you are a CIS contractor. That applies regardless of business size, business structure, or whether you are running one job or a hundred.

Here is what CIS requires, in sequence.

Register as a CIS contractor before your first sub payment

You must register with HMRC as a contractor before you make any payment to a subcontractor for construction work. Register through your HMRC business tax account online. This is not a formality you complete after you have started - it must be in place first.

Verify each subcontractor with HMRC before paying them

Before paying a sub for the first time, verify their CIS status through HMRC's online system. HMRC tells you the applicable deduction rate:

Sub's CIS status	Deduction rate
Gross payment status	0%
Registered under CIS	20%
Not registered under CIS	30%

The deduction applies to the labour element only. Genuine materials and equipment hire paid by the sub are excluded from the deduction base. If a sub invoices £8,000 for labour and £2,000 for materials, you deduct from the £8,000. The amounts deducted go directly to HMRC and count toward the sub's income tax and National Insurance bill - you are collecting their tax, not taking their money.

File monthly returns and pay deductions on time

After each CIS tax month (6th of one month to the 5th of the next):

• Monthly return due: 19th of the following month
• Deductions paid to HMRC: 22nd of the following month

From 6 April 2026, the obligation to file a nil return was reinstated. If you paid no subcontractors in a month, you must still file a nil return or formally notify HMRC of a period of inactivity - missing this now attracts a penalty.

Issue payment and deduction statements to your subcontractors

Within 14 days of each tax month end, send each sub a statement showing the gross amount, the deduction made, and the net paid.

The penalty for missing monthly CIS returns starts at £100 and escalates to £3,000 or 100% of the deductions on that return - whichever is higher. Fail to verify a sub at all and HMRC can assess penalties on the full gross payment, not just the missed deduction.

Set up CIS before the first job and run it every month. Once the process is in place, it is a straightforward monthly task.

VAT and the domestic reverse charge#

You must register for VAT once your taxable turnover exceeds £90,000 in any rolling 12-month period. Register with HMRC as soon as you approach that threshold.

Once VAT-registered and doing B2B construction work, the domestic reverse charge applies to most construction services. Your VAT-registered subcontractors do not charge you VAT on their invoices - you account for it directly to HMRC on your VAT return. This applies within the B2B supply chain; it does not apply to the invoice you raise to your end client.

The practical effect is that sub invoices come in without VAT and you handle the accounting. It keeps the cashflow mechanics clean once you understand it. An accountant who knows construction is worth paying for here.

Insurance#

Employers' liability insurance is legally required under the Employers' Liability (Compulsory Insurance) Act 1969 if you employ anyone - one part-time member of staff is enough to trigger the obligation. Minimum cover: £5 million. The fine for not holding it: £2,500 per day.

Public liability insurance is not a legal requirement but every serious client expects it. You will not win housing association contracts, commercial work or managed property maintenance contracts without it. Treat it as a cost of doing business.

Your subcontractors carry their own public liability cover and are responsible for it on site. Your contracts with them should require proof of appropriate insurance before they start work.

What actually makes contractor arbitrage non-compliant#

Contractor arbitrage is not illegal anywhere in the UK. What gets operators into trouble:

• Not registering for CIS before the first sub payment - HMRC can back-assess penalties on the full gross amounts paid
• Applying the wrong deduction rate (20% versus 30% is a real difference; HMRC collects the shortfall from you, not from the sub)
• Missing monthly CIS returns, including nil returns from April 2026 onwards
• Acting as principal contractor on a higher-risk building without BSR registration under the Building Safety Act 2022
• No employers' liability cover while employing staff - £2,500 per day

None of these are ambiguous. They have known penalties and known fixes. Set the compliance stack up before the first job and every job after that is clean.

The UK is one of the cleaner markets to run this model. No mandatory contractor licence. A tax withholding scheme that, once you understand it, keeps your subs' taxes in order and reduces surprises. Set it up right once and it runs as a monthly process in the background.

Is construction arbitrage the same as contractor arbitrage?#

Yes, same model. Contractor arbitrage is the broader, more commonly searched term - winning work as the main contractor and subcontracting delivery for a margin, across any kind of contracting. Construction arbitrage is that same model narrowed to building, trades and property work specifically.

Construction Arbitrage is where tradespeople and operators learn to win the work, manage the trades, and keep the margin.

For the full breakdown on how the terms relate, see is construction arbitrage the same as contractor arbitrage.

The next step#

The full UK legality detail with CIS tables, VAT reverse charge mechanics, insurance and the building regulations picture lives in is construction arbitrage legal in the UK. For the licensing question compared across all major markets, see do you need a contractor licence for construction arbitrage. If you are ready to set the business up properly, how to start a construction arbitrage business walks through the entity registration, CIS setup and first jobs sequence.

If you want to stay current as CIS rules, VAT thresholds and licensing regulations change, join the mailing list - new posts and updates land there first.

If you want the complete system in one place, THE FAMILY SECRET - How Construction Arbitrage Really Works is coming soon.

FAQ#

Is contractor arbitrage legal in the UK? Yes. Contractor arbitrage (winning the job, subcontracting the work, keeping the spread) is completely legal in the UK. It is standard main contracting. The compliance you need is HMRC's Construction Industry Scheme (CIS) before your first sub payment, and VAT registration once your taxable turnover exceeds £90,000.

Is construction arbitrage the same as contractor arbitrage? Yes, same model. Contractor arbitrage is the broader term for winning work and subcontracting it out for a margin. Construction arbitrage is that same model applied to building, trades and property. Construction Arbitrage is the brand that teaches it.

Do you need a contractor licence for contractor arbitrage in the UK? No mandatory general contractor licence exists in England, Wales, Scotland or Northern Ireland for private construction work. The UK has no national licensing board equivalent to California's CSLB. A government call for evidence on construction licensing ran from May to August 2026, but nothing has been legislated.

What is CIS and does it apply to contractor arbitrage? CIS is HMRC's Construction Industry Scheme. If you pay subcontractors for construction work, you are a CIS contractor. You must register with HMRC before your first sub payment, verify each sub's CIS status, deduct 0%, 20% or 30% from the labour portion of their invoices depending on their status, and file monthly returns.

What are the real legal risks of contractor arbitrage in the UK? Failing to register for CIS before paying subs (HMRC can back-assess penalties on the full gross amount), missing monthly CIS returns including nil returns, acting as principal contractor on higher-risk buildings without Building Safety Regulator registration, and operating without employers' liability insurance if you have employees.

This is general information, not legal or tax advice. CIS rules, VAT thresholds, insurance requirements and licensing regulations change. Verify current requirements with HMRC or a qualified UK construction accountant before you take work.

Last checked: 20 July 2026.