Agentic UK Construction Industry Scheme (CIS) monthly return preparation, subcontractor verification status check schedule, and HMRC penalty appeal letter service for small main contractors and labour-only subcontractors (1–20 staff) required to file CIS300 returns monthly and deduct tax at source from payments to unverified subcontractors. Replaces the bookkeeper or accountant who charges £200–£600/month to verify subcontractors, calculate gross/standard/higher deduction rates, complete the CIS300, and draft HMRC penalty appeals — a process where a single missed return triggers an automatic £100 penalty escalating to £3,000.
Why now
No fresh signal in today's batch; justified by persistent r/Construction and r/smallbusiness complaints about CIS penalty notices and HMRC's CIS compliance campaigns. HMRC's own figures show CIS penalties issued to small contractors are rising year-on-year, and the Construction Leadership Council has flagged CIS admin burden as a top-three compliance pain point for micro-contractors.
Commercial value
HMRC estimates 150,000+ contractors registered under CIS. Small main contractors (1–20 staff) typically pay a bookkeeper £200–£600/month for CIS admin; target ACV £1,200–£3,600/yr. Budget line: 'bookkeeper / accountant CIS fees.' TAM: even 5,000 customers at £150/mo = £9m ARR. High repeat revenue because CIS300 is filed every month without exception.
Go-to-market
Target UK small main contractors via Facebook groups (UK Construction Network, 1000s of members), FMB (Federation of Master Builders) forums, and direct outreach to sole-trader builders on Checkatrade/MyBuilder. Hook: 'Never miss a CIS300 deadline again — £99/mo, we file it for you.' First 10 customers via FMB regional WhatsApp groups. Price: £99/mo for up to 10 subcontractors, £149/mo up to 30.
2-week MVP
Intake form collects contractor UTR, list of subcontractors paid that month (name, UTR, gross payment), and payment dates. GPT-4o chain verifies deduction rate logic and outputs a pre-filled CIS300 summary sheet plus a formatted HMRC online filing instruction checklist. Human-in-the-loop: founder manually submits via HMRC portal on customer's behalf for first 10 customers. Cut: direct HMRC API integration, automatic bank feed import, subcontractor portal. Day-1 outcome: a sole-trader builder pays £99 and receives a complete, accurate CIS300 ready to file — avoiding the £100 automatic penalty they got last quarter.
Agent score
0.61 — Commercial score is 0.82: monthly recurring need, named bookkeeper budget line, large addressable base of 150k+ CIS-registered contractors, believable £1,200+ ACV — strong. Speed is 0.85: MVP is intake form + LLM output + manual filing, shippable in under 2 weeks, first customers reachable via free Facebook/WhatsApp construction groups. Defensibility 0.45: moat builds slowly through subcontractor verification history and monthly data lock-in, but the core logic is replicable; score would rise to 0.65+ if integrated with accounting software (Xero/QuickBooks) after 6 months.
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