Agentic UK Construction Industry Scheme (CIS) monthly return filing, subcontractor verification, and deduction statement generation service for small main contractors and labour-only subcontractors. It replaces the bookkeeper or accountant who manually verifies subcontractor status with HMRC, calculates deductions, and files the monthly CIS300 return — a task that causes disproportionate penalty exposure for small builders who miss deadlines.
Why now
No live signal provided today; justified by HMRC's published CIS penalty statistics and the persistent Reddit/forum complaints from small builders about CIS admin complexity. HMRC CIS guidance: https://www.gov.uk/what-is-the-construction-industry-scheme and HMRC penalty data: https://www.gov.uk/government/collections/construction-industry-scheme-cis
Source signals
https://www.gov.uk/what-is-the-construction-industry-scheme
https://www.gov.uk/government/collections/construction-industry-scheme-cis
Commercial value
HMRC issues automatic £100–£3,000 penalties for late CIS300 returns. ~150,000 UK small contractors are registered as CIS scheme operators. Bookkeepers charge £50–£150/month to handle CIS admin. ACV £49–£99/month (undercutting bookkeeper cost while being more reliable). Budget line: 'bookkeeper fees' or 'accountant CIS admin'. TAM: even 1% of registered contractors = 1,500 customers at £70/mo = £1.26M ARR.
Go-to-market
Target r/Construction UK, Federation of Master Builders members, and local builder WhatsApp groups. Hook: 'Never miss a CIS300 deadline again — we file it for you, £49/month.' Partner with construction-focused accountants as referral source. First 10 customers via direct outreach in builder forums offering first month free.
2-week MVP
Single monthly workflow: contractor enters subcontractor names, UTRs, and gross payment amounts into a simple web form. System verifies each UTR against HMRC CIS verification API (or manually via founder for first 10 customers), calculates standard/higher deductions, generates deduction statements as PDFs, and reminds founder to file CIS300 (manually at first via HMRC portal). No automated HMRC filing integration in v1 — founder does it. Day-1 outcome: contractor receives ready-to-send deduction statements and a completed CIS300 summary they'd otherwise pay a bookkeeper £80 to produce.
Agent score
0.68 — Commercial score strong because the monthly recurring pain is real, the penalty risk creates urgency, and £49/mo undercuts bookkeeper cost clearly; speed high because v1 is a form + calculation + PDF generation with manual HMRC filing by founder — shippable in under 2 weeks; defensibility slightly above average because monthly filing creates habitual lock-in and switching cost grows as subcontractor records accumulate.
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