CIS Construction Industry Accountants London

GM Professional Accountants is a firm of CIS Construction Industry Accountants London contractors and subcontractors rely on for monthly returns, deduction verification and tax refund claims. If you are unsure whether you should be deducted at 20%, 30% or 0%, or you have not filed a Self Assessment return since starting CIS work, our team based in Old Street and Ilford can review your position and correct it before HMRC does.

The Construction Industry Scheme (CIS) is HMRC’s system requiring contractors to deduct tax at source, 20% for registered and 30% for unregistered subcontractors, from payments for construction work, before passing it to HMRC monthly.

What Is the Construction Industry Scheme (CIS)?

The Construction Industry Scheme is a tax deduction framework set up by HMRC where contractors deduct money from a subcontractor’s pay before it reaches them, and pass it directly to HMRC as an advance payment towards that subcontractor’s tax and National Insurance.

Both contractors and subcontractors are legally required to register before work begins. Contractors who fail to register or deduct correctly can face HMRC penalties, while unregistered subcontractors are deducted at the higher 30% rate rather than 20%. You can read the full framework directly on HMRC’s Construction Industry Scheme guidance.

CIS covers most construction related work including building, groundwork, demolition, electrical and plumbing installation, painting and decorating, and repairs. It does not apply to architecture, surveying, scaffolding hire alone, or delivering materials with no other construction role.

Who Needs a CIS Accountant in London?

Whether you are a sole trader labourer, a subcontracted electrician, or a limited company running multiple construction crews, CIS creates ongoing compliance obligations that a general accountant without construction industry experience often misses. See how we support growing firms on our Small Business Accountants for Construction Companies in London page.

How Do CIS Deduction Rates Work in 2026?

There are three possible CIS deduction rates, and which one applies to you depends entirely on your registration and compliance status with HMRC.

Source: HMRC Construction Industry Scheme guidance, gov.uk. Gross payment status turnover tests apply per director for limited companies, so a five-person Ltd company needs at least £150,000 in qualifying turnover.

What Are the CIS Filing Deadlines and Penalties?

Contractors must submit their CIS300 monthly return to HMRC by the 19th of every month, covering deductions made in the previous tax month, with payment due by the 22nd if paying electronically. Missing the return deadline triggers an automatic £100 penalty, rising the longer it remains outstanding.

Subcontractors are not off the hook either. Even with tax already deducted at source, you must still submit an annual Self Assessment return by 31 January, or you risk losing your tax-free Personal Allowance and any entitlement to work expense relief.

HMRC has also confirmed further changes affecting CIS subcontractors from April 2026. We have covered the specifics in our CIS changes from April 2026 in London guide.

How Does the Domestic VAT Reverse Charge Affect Construction Businesses?

Since 1 March 2021, the domestic VAT reverse charge has applied to most construction services between VAT-registered CIS businesses. Instead of the supplier charging VAT, the customer accounts for it directly on their own VAT return, which prevents missing trader VAT fraud within the supply chain.

This changes how invoices must be worded and can significantly affect cash flow, since subcontractors no longer collect VAT from contractors to hold until their VAT return is due. Full detail is available in HMRC’s VAT reverse charge notice for building and construction services.

What HMRC Changes to CIS Are Coming in 2026 and 2027?

Making Tax Digital for Income Tax begins affecting self-employed subcontractors and landlords with qualifying income above £50,000 from April 2026, extending to those above £30,000 from April 2027. If you are a CIS subcontractor operating as a sole trader, this means quarterly digital updates to HMRC rather than a single annual Self Assessment return.

HMRC has also continued tightening the compliance tests attached to gross payment status, meaning subcontractors need cleaner VAT and PAYE records than in previous years to retain 0% deduction status.

How Can I Claim Back Overpaid CIS Tax?

CIS deductions are offset against your final tax bill through your Self Assessment return. If the amount deducted at source is higher than your actual tax and National Insurance liability, HMRC refunds the difference. Common allowable expenses that reduce your tax bill and increase your refund include:

1. Accountancy and professional fees

2. Work travel and vehicle running costs

3. Materials and tools purchased for jobs

4. Protective clothing and equipment required on site

5. General running costs such as insurance, phone and advertising

Many subcontractors underclaim simply because they never see an accountant who understands the sector. This is where a specialist CIS Construction Industry Accountants London team makes a measurable difference to the size of your refund.

Why Choose GM Professional Accountants as Your CIS Construction Industry Accountants London Team?

GM Professional Accountants is an AAT-regulated firm serving contractors and subcontractors from our Old Street office in Central London and our Ilford base covering East London and Essex. We confirm coverage across London and Essex for every CIS client, whether you are based near Canary Wharf, Wimbledon or Loughton.

Rather than charging by the hour, we work on fixed monthly packages so you always know your cost upfront, backed by a team that has handled construction industry compliance work for years and been recognised with multiple industry awards.

Frequently Asked Questions