What CIS Returns Involve — and Why UK Contractors Struggle with Them
The Construction Industry Scheme (CIS) requires contractors to deduct tax at source from payments to subcontractors and pay those deductions to HMRC monthly. It applies to any business that pays subcontractors for construction work — from small sole trader builders to large property developers.
The monthly CIS process involves more steps than most contractors expect:
- Subcontractor verification: Before paying a new subcontractor for the first time, the contractor must verify their CIS status with HMRC. This determines the deduction rate — 20% for registered subcontractors, 30% for unregistered, 0% for those with gross payment status.
- Payment calculation: For each payment, the contractor identifies the materials element (no CIS deduction) and the labour element (CIS deduction applies). The deduction is calculated on the labour/profit portion only.
- Monthly CIS300 return: By the 19th of each month (22nd for electronic payment), the contractor must submit a CIS Monthly Return (CIS300) to HMRC listing every subcontractor paid in the previous tax month, the gross amount, the deductions made, and the net payment.
- Subcontractor payment statements: Each subcontractor must receive a written statement showing the gross amount, CIS deduction, and net payment each time they are paid.
- Annual CIS summary: At year end, a summary of all CIS deductions made during the tax year is required.
What an Indian CA Firm Handles in the CIS Process
The division of CIS work between an Indian CA team and the UK contractor mirrors the same pattern as MTD submissions and RTI — preparation is handled in India, submission requires UK HMRC access.
| CIS Task | Indian CA Team | UK Contractor or Agent |
|---|---|---|
| Subcontractor verification preparation | Prepares verification request data | Submits via HMRC CIS online |
| Deduction rate calculation (20% / 30% / 0%) | Applies correct rate based on verification result | Not required |
| Labour vs materials split | Calculated per invoice — CIS deduction on labour only | Confirms materials figures if invoices unclear |
| Monthly CIS300 data preparation | Prepares complete return data for all subcontractors | Reviews and submits by 19th of month |
| Subcontractor payment statements | Prepares and delivers | Forwards to subcontractors |
| CIS deduction posting in accounts | Codes CIS deductions correctly in Xero/Sage | Not required |
| Annual CIS summary preparation | Prepared for year end | Not required |
| CIS deduction offset against PAYE liability | Calculates offset in payroll summary | Applies when making PAYE/NIC payment |
The Monthly CIS300 Return — Who Prepares and Who Submits
The CIS300 Monthly Return is the core document in CIS compliance. Your Indian CA team prepares all the data — subcontractor details, gross payments, deductions applied, and net payments for the tax month (6th of one month to 5th of the next).
Submission options:
- Via HMRC CIS online: You log into your HMRC business account and submit the prepared CIS300 data. Takes 10–15 minutes once the data is ready. Deadline: 19th of each month.
- Via payroll software: Xero Payroll, Sage, and BrightPay all support CIS300 submission directly to HMRC. Your Indian team prepares data within or alongside the software; you authorise and submit.
- Via UK-registered CIS agent: Your UK accountant or a payroll bureau acts as CIS agent and submits on your behalf. Your Indian team provides them with the prepared data.
- Via Indian firm if HMRC-registered: If your Indian CA firm holds HMRC payroll agent registration covering CIS, they can submit the CIS300 directly after you grant agent authorisation through your HMRC account.
CIS Deductions, Verification, and Subcontractor Payslips
Getting the deduction rate right matters. Applying 20% when HMRC says 30% means you underpay — creating a liability. Applying 30% when the subcontractor is gross-status creates unnecessary deductions and disputes with your subbies.
Verification Process
Before paying a new subcontractor for the first time in a tax year, you must verify their CIS status. Your Indian CA team prepares the verification request with the subcontractor's UTR (Unique Taxpayer Reference), legal name, and trading name if different. You submit via HMRC CIS online. HMRC returns the verification number and deduction rate. Your Indian team records this and applies it to all future payments in the tax year.
Deduction Rates
| Subcontractor Status | Deduction Rate | When It Applies |
|---|---|---|
| Registered with gross payment status | 0% | HMRC has approved the subcontractor to receive gross payments — they pay their own tax directly |
| Registered under CIS (standard) | 20% | Subcontractor is registered with HMRC under CIS but does not have gross payment status |
| Unregistered | 30% | Subcontractor cannot be verified or is not registered with HMRC |
CIS + Standard Bookkeeping — The Combined Package
For UK construction businesses, the most practical arrangement is combining CIS administration with standard bookkeeping services. The same Indian CA team that reconciles your bank accounts also handles CIS — there is no handover friction between the two services.
A combined construction bookkeeping and CIS package from an Indian CA firm covers:
- Transaction coding and bank reconciliation (including CIS payment coding)
- VAT return preparation on a standard or cash accounting basis
- Reverse charge VAT for construction services — correctly applied since October 2020
- CIS verification preparation, deduction calculations, and payment statements
- Monthly CIS300 data preparation
- Monthly management accounts with gross margin by project if required
- Payroll preparation if you also have PAYE employees alongside CIS subcontractors
The reverse charge VAT rule — where the VAT on construction services is accounted for by the customer rather than the supplier — requires correct identification of which services are covered. Your Indian CA team applies this correctly, which is an area where errors are common among bookkeepers without specific construction sector experience.
Cost: UK Accountant vs Indian CA Firm for CIS
| Scope | UK Accountant / Bureau | Indian CA Firm | Annual Saving |
|---|---|---|---|
| CIS returns only (up to 5 subcontractors) | £80–£150/month | £40–£65/month | £480–£1,020 |
| CIS returns (6–15 subcontractors) | £120–£220/month | £65–£100/month | £660–£1,440 |
| CIS + bookkeeping + VAT (small contractor) | £350–£600/month | £120–£200/month | £2,760–£4,800 |
| CIS + bookkeeping + VAT + payroll (PAYE employees) | £500–£850/month | £180–£280/month | £3,840–£6,840 |
For UK construction businesses currently managing CIS manually or paying a UK accountant separately for CIS and bookkeeping, combining both services with an Indian CA firm typically saves £3,000–£6,000 per year on a like-for-like scope comparison.
Written by Sharma Jyoti, CA (ICAI) — Founder, Sharma Jyoti and Co. We are an ICAI-registered Chartered Accountant firm providing outsourced bookkeeping and accounting services to Australian, US, UK and Canadian businesses. Our team includes Xero Advisor Certified professionals (Certificate #17207818). Learn more about our firm →