Is Construction Arbitrage Legal in the UK?

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

I run this model. The UK has its own compliance layer - CIS - that the US and Australia do not have, and getting it right is non-negotiable. Here is exactly what the law asks of you.

Why construction arbitrage is legal in the UK#

Construction arbitrage is standard main contracting. You enter the prime contract with the client, subcontract the physical work to vetted trades, and keep the spread between what the client pays and what the work costs you to deliver. That structure is how every major development, every commercial fit-out, and most large residential projects are delivered in the UK.

There is no law in England, Wales, Scotland or Northern Ireland that requires a main contractor to self-perform any portion of a private construction contract. The obligation the law places on you as the prime is to be responsible for the delivered result, carry appropriate insurance, and - in the UK specifically - comply with HMRC's tax withholding system for subcontractor payments.

The model is legitimate. What makes it legitimate is doing it with the compliance stack in place.

No mandatory contractor licence in the UK#

This is where the UK differs significantly from the US and Australia. 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 you can enter a prime contract on a private job.

The UK does have voluntary schemes - TrustMark and the Construction Skills Certification Scheme (CSCS) - and clients often ask for them, but they are not a legal requirement for acting as the main contractor on private work.

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: The Building Safety Act 2022 introduced a registration regime for buildings 18 metres or taller, or 7 or more storeys. If you are acting as the principal contractor on one of these, you must be registered with the Building Safety Regulator at HSE and meet specific competence and mandatory occurrence reporting requirements.
• Asbestos: Any work involving disturbance of asbestos-containing materials requires a licence from the Health and Safety Executive.
• Upcoming consultation: In May 2026, the Ministry of Housing, Communities and Local Government launched a consultation on potentially extending mandatory licensing to subcontractors on domestic work. Nothing has been legislated as of today; the consultation is open.

For private, non-specialist, non-higher-risk work, you can enter the prime contract without holding a mandatory general contractor licence. The compliance that matters is what follows.

CIS - the compliance that matters most in the UK#

The Construction Industry Scheme (CIS), run by HMRC, is the most significant compliance requirement the UK has that the US and Australia do not. If you are paying subcontractors for construction work, you are a CIS contractor - full stop. The scheme applies regardless of your business size or structure.

Here is what CIS requires, in sequence.

Register as a contractor before your first sub payment#

You must register with HMRC as a CIS contractor before you make any payment to a subcontractor. Registration is done online through your HMRC business tax account. This is not a formality you complete after your first job - it must be in place first.

Verify each subcontractor with HMRC before paying them#

Before you pay a sub for the first time, you verify them through HMRC's CIS online system. HMRC tells you the applicable deduction rate for that sub:

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 £10,000 for labour and £3,000 for materials, you deduct from the £10,000 only.

The amounts you deduct go directly to HMRC and count toward the sub's income tax and National Insurance bill. You are not taking money from the sub - you are forwarding their tax payments.

File monthly returns and pay deductions to HMRC#

After each tax month (which runs from the 6th of one month to the 5th of the next):

• Monthly return: due by the 19th of the following month. From 6 April 2026, you must also file a nil return in any month where you made no sub payments, or formally notify HMRC of a period of inactivity. Failing to do either now attracts a penalty.
• Pay the deductions: due to HMRC by the 22nd of the following month (19th if paying by post).

Issue payment and deduction statements to your subcontractors#

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

The penalty picture: missing monthly CIS returns starts at £100 and escalates to £3,000 or 100% of the CIS deductions on the return - whichever is higher. If you fail to verify a sub at all, HMRC can assess penalties on the full gross payment, not just the missed deduction. Set up CIS before the first job, run it every month. It is a straightforward monthly task once it is in place.

VAT and the domestic reverse charge#

If your taxable turnover exceeds £90,000 in any rolling 12-month period, you must register for VAT with HMRC.

Once VAT-registered, a specific rule applies to most construction services between VAT-registered businesses: the domestic reverse charge. Under the VAT domestic reverse charge for building and construction services - which has applied since March 2021 - VAT-registered subcontractors do not charge you VAT on their invoices for most construction labour. Instead, you account for the VAT directly to HMRC.

The practical effect: you receive sub invoices without VAT added, and you account for the VAT yourself as both input and output on your VAT return. HMRC introduced this to close a common VAT fraud where contractors collected VAT from clients and never remitted it.

The reverse charge applies where both the customer (you) and the supplier (your sub) are VAT-registered and the customer is making onward supplies of construction services. It does not apply on the invoice you raise to your end client - only within the B2B supply chain.

Business registration and tax#

Register your business entity before you take your first contract:

• Limited company: register through Companies House. Corporation Tax applies to company profits; register with HMRC for Corporation Tax within three months of starting to trade.
• Sole trader: register for Self Assessment with HMRC. Profits are subject to Income Tax and Class 2 and Class 4 National Insurance.

Subcontractor payments are business expenditure, subject to CIS deduction as above, and run through your normal accounts. They do not go through payroll.

Insurance requirements#

Employers' liability insurance is legally required under the Employers' Liability (Compulsory Insurance) Act 1969 if you employ anyone - even one part-time member of staff. The legal minimum cover is £5 million. Failure to hold it is a fine of £2,500 per day. You must display or make available your certificate of insurance at your place of business.

Public liability insurance is not a legal requirement in the UK. It is, however, expected by virtually every commercial client, every developer, and most domestic clients with any experience. You will not win serious work without it. Treat it as a cost of doing business.

Professional indemnity insurance may also be required where you are providing design input or specifications alongside the build. Check your client contracts carefully.

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

What actually makes it non-compliant#

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

• Failing to register 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, and HMRC collects the shortfall from you, not the sub
• Missing monthly CIS returns - the nil return requirement from April 2026 means even inactive months require filing or a notification
• Acting as principal contractor on higher-risk buildings without BSR registration - a legal breach under the Building Safety Act 2022
• No employers' liability insurance while employing staff - £2,500 per day, every day you are exposed

None of these are ambiguous. They are known requirements with known penalties and known fixes.

The UK is one of the cleanest markets in the world to run this model. No mandatory contractor licence. A tax scheme in CIS that, once you understand it, reduces your admin and keeps subs' taxes in order. Set it up right once and every job is clean.

The next step#

If you are mapping the global picture, the legality overview across every major market covers the US, Canada and Australia alongside the UK. For the licensing question worldwide, do you need a contractor licence for construction arbitrage goes through every jurisdiction. And for the full setup sequence - entity, CIS registration, insurance, first clients and first subs - see how to start a construction arbitrage business.

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

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

Last checked: 14 June 2026.