The verdict in three sentences
For a London main contractor running 400 subcontractors, chasing CIS details, insurance certificates and RAMS by email is no longer an admin chore, it is a tax and safety exposure. A custom subcontractor portal with automatic 30-day reminders, expiry checks and payment holds brings the work down to a few hours a month and leaves an audit trail for HMRC and the HSE. Plan for 3 to 4 months and a Kolonell budget of 2,500,000 to 15,000,000+ FCFA (EUR 3,810 to 22,870+) depending on complexity, with anything beyond that set in the quote.
What UK compliance actually requires from the contractor
Under the Construction Industry Scheme (CIS), a contractor must verify each subcontractor with HMRC before the first payment, then deduct 20% for registered subcontractors, 30% for unverified ones, or nothing for those with gross payment status. Getting it wrong makes the contractor liable for the tax that should have been deducted, and the monthly CIS return carries penalties from GBP 100 when filed late. On top of tax, CDM 2015 requires the principal contractor to check that each trade has suitable risk assessments and method statements (RAMS) and competent workers, usually evidenced by CSCS cards.
With 400 subcontractors and an average of five documents each, renewed once or twice a year, the commercial team handles more than 3,500 documents a year.
| Document | Check frequency | How it is verified | Risk if missing or expired |
|---|---|---|---|
| CIS verification | Before first payment, then if not paid for 2 tax years | HMRC online service, verification number | Contractor liable for under-deducted tax |
| Employers' liability insurance | Annual | Certificate, minimum GBP 5m cover by law | Uninsured injury claims on site |
| Public liability insurance | Annual | Limit, often GBP 5m to 10m required | Third-party claims fall back on the contractor |
| RAMS per package | Before start of works | Review by site manager | CDM breach, HSE enforcement |
| CSCS cards of operatives | On site induction | Card check or app | Unqualified workers on site |
| Health and safety accreditation (CHAS, SafeContractor) | Annual | Membership certificate | Failed pre-qualification on public frameworks |
| Right to work evidence | At engagement | Declaration and checks | Civil penalties up to GBP 60,000 per illegal worker |
Off-the-shelf platform or custom portal
SaaS compliance platforms handle the standard case well: the subcontractor uploads, the tool tracks expiry dates. Their limits show when the contractor wants to hold a payment in its construction ERP, think per project and per package rather than per supplier, or apply its own rules on second-tier subcontracting and client approvals.
| Criterion | SaaS platform (2026 order of magnitude) | Kolonell custom portal |
|---|---|---|
| Cost | GBP 2,500 to 8,000 a year | 2,500,000 to 15,000,000+ FCFA (EUR 3,810 to 22,870+), rest in the quote |
| Time to go live | 2 to 6 weeks | 3 to 4 months |
| ERP and accounts link | Standard connectors, often CSV export | Direct link, payment hold when a document is missing |
| Project view | Rarely available | Dashboard per project and package |
| Business rules | Generic | CIS status, second tier, client approval, RAMS sign-off |
| Data ownership | With the vendor | Dedicated database, UK or EU hosting |
| Maintenance | Included in subscription | 35,000 to 120,000 FCFA a month (EUR 53 to 183) |
Over five years, a GBP 5,000 annual subscription adds up to GBP 25,000 with no ownership. Custom work makes sense when the portal must talk to your ERP and drive payments; if you only need a document vault, a SaaS tool is often enough.
Features to put in the specification
The useful scope fits in a few blocks: a subcontractor area with email and SMS invitations, uploads with automatic reading of expiry dates, storage of the CIS verification number and deduction rate, reminders at 30, 15 and 7 days, and a payment hold when a document is still missing. Site managers get a per-project view showing who may start work, and RAMS are approved in the tool with a named sign-off. Every action is time-stamped to build an audit trail.
| Phase | Duration | Deliverable |
|---|---|---|
| Scoping and compliance rules | 2 to 3 weeks | Document matrix per trade, mock-ups |
| Subcontractor area and uploads | 4 weeks | Invitations, uploads, date extraction |
| Reminders and dashboards | 3 weeks | 30-day alerts, project view, RAMS approval |
| ERP link and payment hold | 3 to 4 weeks | Supplier sync, CIS rate on payment runs |
| Testing and onboarding of 400 subcontractors | 2 to 3 weeks | Invitation campaign, team training |
Mini case study
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Emma, commercial director of a 280-person main contractor in London, estimates that subcontractor compliance takes 0.8 FTE today. At GBP 38,000 fully loaded, that is GBP 30,400 a year. Once the portal is live, residual work (exceptions, disputes) drops to 0.2 FTE, or GBP 7,600, a saving of GBP 22,800 a year. Assuming a medium-complexity project at the top of the range, EUR 10,670, plus Standard maintenance of 75,000 FCFA a month (EUR 114, so EUR 1,368 a year), the build is paid back well within the first year, before counting a single avoided CIS liability.
FAQ
Can the portal check CIS status automatically?
The portal stores the HMRC verification number, deduction rate and date, and flags subcontractors that need re-verification after 2 tax years without payment. Where API access is available, the check runs without manual input; otherwise it takes about 2 minutes per subcontractor.
What happens if a subcontractor misses a deadline?
Reminders go out at 30, 15 and 7 days by email and SMS. On expiry, the status turns red on the project and the payment is held in the ERP until the document is uploaded.
How long does it take to onboard 400 subcontractors?
Allow 4 to 6 weeks with an invitation campaign and targeted phone follow-up. On this kind of project, around 70% of subcontractors upload their documents in the first month.
Are second-tier subcontractors covered?
Yes, a subcontractor can declare its own subcontractors, who get limited access. The main contractor keeps visibility over the full chain, which helps with client approvals on frameworks.
Where is the data hosted?
Hosting is in the UK or EU and compliant with UK GDPR. Retention is configurable, often 6 years after the contract ends to match tax record requirements.
Let's scope your project. We define with you the number of subcontractors, the documents tracked and the ERP link for a portal delivered in 3 to 4 months. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
