Accountants for Construction CIS Business

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— Construction Industry Scheme Specialists Accountants for Construction CIS Business in London and Essex Written by Sharaz Zaman, Founder of GM Professional Accountants, AAT Member, London accountant since 2012. Updated in September 2026.

If you run a construction business anywhere from Ilford to Wimbledon, you need accountants for construction CIS business who understand deductions, gross payment status and monthly returns from day one, not accountants who learn CIS on your file. GM Professional Accountants handles CIS registration, monthly CIS300 returns, VAT reverse charge compliance and subcontractor tax refunds for contractors and subcontractors across London and Essex. The next CIS300 filing deadline is the 19th of every month, and missing it triggers an automatic £100 HMRC penalty on day one.

What is CIS, in one sentence: The Construction Industry Scheme is an HMRC framework requiring contractors to deduct tax at 20%, 30% or 0% from subcontractor payments before passing the money to HMRC as an advance on the subcontractor’s tax and National Insurance.

Key Takeaways

1. Registered subcontractors have 20% deducted, unregistered subcontractors have 30% deducted, and gross payment status subcontractors have 0% deducted.

2. Businesses spending over £3 million on construction in 12 months must register as deemed contractors even outside the construction sector.

3. Missing a CIS300 return by the 19th of the month triggers an automatic £100 fixed penalty, rising to £200 and beyond.

4. MTD for Income Tax becomes mandatory for self-employed subcontractors earning over £50,000 from April 2026, and over £30,000 from April 2027.

What Is the Construction Industry Scheme and Does My Business Need to Register?

The Construction Industry Scheme applies to most building work in the UK, including site preparation, demolition, alterations, repairs and decorating. You must register as a contractor if you pay subcontractors for construction work, or if your business is not construction based but has spent more than £3 million on construction in the 12 months since your first payment. This second category catches property developers, housing associations and even some retailers who commission large fit-out projects without realising CIS applies to them. Subcontractors are not legally required to register, but unregistered subcontractors have tax deducted at the higher 30% rate rather than the standard 20%. This single decision has a direct effect on monthly cash flow, which is why finding accountants for construction CIS business early, before your first subcontractor payment, saves money from month one. Our team registers both contractors and subcontractors and verifies subcontractor status directly with HMRC before the first payment is made.

How Much Tax Does CIS Deduct From Subcontractor Payments?

There are three CIS deduction rates set by HMRC. Registered subcontractors have 20% deducted from labour payments. Subcontractors who have not registered for CIS have 30% deducted. Subcontractors who hold gross payment status have 0% deducted and are paid in full, settling their own tax and National Insurance through Self Assessment. Materials, VAT and certain expenses are excluded from the deduction calculation, and getting this split wrong is one of the most common CIS errors we see when we take on a new construction client. These deductions count as advance payments towards the subcontractor’s tax bill, which is why many subcontractors are due a refund at the end of the tax year once actual expenses and allowances are accounted for.

What Is Gross Payment Status and How Do I Qualify?

Gross payment status means HMRC pays you in full with no CIS deduction, which can transform cash flow for a growing construction business. To qualify, HMRC requires you to prove a track record of paying tax and National Insurance on time, run your business through a UK bank account, and meet a minimum turnover test based on your business structure. Limited companies, partnerships and sole traders can all apply, but the application is assessed on compliance history, so a single missed VAT or Self Assessment deadline in the past 12 months can result in refusal. We prepare gross payment status applications for London and Essex construction clients as part of our CIS onboarding process, and we monitor ongoing compliance so status is not lost through an avoidable late filing. Gross payment status removes the deduction, but it does not fix every cash gap. On projects paid in stages, retentions held back until practical completion can still leave money tied up for months, which we cover in our guide to WIP, retentions and cash flow on staged income.

How Does the VAT Domestic Reverse Charge Affect CIS Contractors?

Since March 2021, the domestic reverse charge for building and construction services has applied to most CIS registered supplies between VAT registered businesses. Under the reverse charge, the subcontractor no longer charges VAT on their invoice. Instead, the contractor accounts for that VAT directly to HMRC on their own VAT return. This was introduced to close a fraud gap, but it also means subcontractors receive invoices with no VAT added, which can tighten cash flow if it is not planned for. Getting the reverse charge wrong on an invoice is one of the most common compliance mistakes we correct for new clients moving from a generalist accountant to a construction industry CIS specialist. For the full mechanics of when the reverse charge does and does not apply, read our guide on how the reverse charge hits construction cash flow.

What CIS Deadlines and Penalties Should Construction Businesses Know in 2026?

Every contractor must file a CIS300 monthly return by the 19th of the month following the return period. According to HMRC’s own compliance handbook, a return filed even one day late triggers an automatic £100 fixed penalty. If the return is still outstanding two months after the deadline, a further £200 penalty applies, and penalties can escalate to £300 or more, with a cap of £3,000 in serious cases. We are seeing a rise in these penalties among Essex and East London construction firms in 2026, largely from missed filings during busy site periods. For full detail on the penalty structure, HMRC publishes the current rules on its CIS late filing penalty guidance. We also cover the local pattern in our post on why Essex and East London construction firms are picking up CIS penalties in 2026.

Sole Trader or Limited Company: Which Structure Saves More Tax Under CIS?

CIS applies whether you trade as a sole trader, partnership or limited company, but the tax outcome differs. Sole traders pay Income Tax and Class 4 National Insurance on profits, with CIS deductions offset against the final bill through Self Assessment. Limited company subcontractors have CIS deducted from the company, then offset against the company’s Corporation Tax and PAYE liabilities, which usually means a faster route to reclaiming overpaid deductions. Section 24 mortgage interest restrictions and IR35 status checks can also affect the decision for contractors working through their own limited company on larger sites. There is no single right answer, and the correct structure depends on turnover, subcontractor volume and long-term growth plans. Whichever structure you use, the value placed on unfinished jobs at your year end changes the profit you are taxed on, so it helps to know how to calculate construction WIP before comparing the two. We walk through the full comparison in our guide on construction sole trader vs limited company structures.

How Do CIS Accounting Options Compare?

Approach	CIS Return Accuracy	Reverse Charge Handling	Gross Payment Support
Filing it yourself	High penalty risk	Manual, error prone	Not offered
A generalist accountant	Variable	Often missed	Rarely proactive
GM Professional Accountants	Filed and verified monthly	Built into every invoice review	Application and ongoing monitoring

Why Choose GM Professional Accountants for Your Construction CIS Business?

GM Professional Accountants is an AAT regulated firm led by Sharaz Zaman, with over 15 years of London accounting experience focused on construction, property and trades businesses. We serve clients across London and Essex, with teams based at Old Street in Central London, Wimbledon in West London, Ilford in East London, and Loughton in Essex. Every construction client gets monthly CIS300 filing, subcontractor verification, VAT reverse charge review and gross payment status support built into a fixed monthly fee, so there are no surprise bills at year end.

What HMRC Changes Are Coming for Construction Businesses in 2026 and 2027?

The most significant change affecting CIS subcontractors is Making Tax Digital for Income Tax. From April 2026, self-employed subcontractors and landlords with qualifying income over £50,000 must keep digital records and submit quarterly updates to HMRC through MTD compatible software. From April 2027, this extends to anyone with qualifying income over £30,000. For a self-employed subcontractor used to a single annual Self Assessment return, this is a major shift in reporting frequency, and construction businesses should plan software and bookkeeping changes well before their mandation date rather than in the month it applies.

Frequently Asked Questions

Do I need an accountant if I am a CIS subcontractor?

You are not legally required to have one, but an accountant for construction CIS business checks whether you are due a refund, confirms your deduction rate is correct, and files your Self Assessment on time to avoid HMRC penalties.

Can I get a CIS tax refund and how long does it take?

Most subcontractors who have had CIS deducted are due a refund once expenses are offset. HMRC typically processes refunds within four to eight weeks of a correctly filed Self Assessment return, though this can take longer during peak filing periods.

What happens if I do not register for CIS as a contractor?

If you meet the criteria to register as a contractor and do not, HMRC can issue penalties and deduct tax at the higher unregistered rate from any subcontractor payments, backdated where non-compliance is identified.

Does CIS apply to a limited company subcontractor?

Yes. CIS applies to sole traders, partnerships and limited companies alike. A limited company has CIS deducted from payments received, then offsets this against its Corporation Tax and PAYE liabilities rather than through Self Assessment.

Do you help construction businesses outside London and Essex?

Our core teams are based in Old Street, Wimbledon, Ilford and Loughton, and we serve construction clients across London and Essex, with remote CIS support available further afield.

Get CIS Right the First Time Book a free consultation with GM Professional Accountants and stop guessing at CIS deductions, gross payment status and monthly deadlines. Book Consultation View Our Services

Sharaz Zaman is the Founder of GM Professional Accountants, an AAT regulated firm serving construction, property and trades businesses across London and Essex, with over 15 years of London accounting experience.