Supreme Operating System → Vertical #12 — ir35.law
Vertical #12 of 15
Pre-Build · Q1 2027 Launch

ir35.law

AI IR35 status determination · CEST 8-factor scoring · SDS generation · FCSA payroll routing via WeSwitchPayroll
3.2m
UK contractors affected
£82k
Avg HMRC liability risk
82%
OS reuse
£754k
Y1 ARR target
116×
Return multiple

The play in one line

AI runs CEST's 8-factor test, produces a defensible Status Determination Statement, and routes every "inside" determination to WeSwitchPayroll's FCSA-accredited umbrella panel — earning a referral fee on every conversion. Three audiences at three price points: contractor (self-serve £19/mo), hirer (£49-99/mo), agency (£199/mo + SafeRec integration). Supply side is already live via existing weswitchpayroll.co.uk relationship. The SDS acknowledgement chase system (s61P ITEPA 2003 — 31-day window) is the retention engine.

Three audiences · Three price points
Contractor
£19/mo
Self-serve CEST assessment · SDS download · WeSwitchPayroll routing on inside determination · take-home calculator
Hirer / Engager
£49–99/mo
Multi-contractor dashboard · SDS issue + chase tracking · s61P ITEPA 2003 compliance · India QA on borderline cases
Agency
£199/mo
SafeRec API integration · bulk SDS issuance · FCSA referral dashboard · white-label for agency clients
Strategy & specification
Context

CLAUDE.md

Session context — market, products, rules, cross-references. Read first in any Claude session.

Strategy

Strategy

Full thesis · off-payroll legislation history · three-audience model · FCSA panel economics · competitive moat

Architecture

Tech Reuse Blueprint

82% OS reuse proof · snap-tool mapping · £6,500 build cost breakdown · 116× return multiple

Product

Product Spec

User journeys · CEST 8-factor weights · SDS template · WeSwitchPayroll referral flow · SafeRec integration

Technical

Developer Spec

Full API spec · database schema · CEST scoring engine · determination logic · SDS chase automations

Execution

Build Plan

6-week sprint · task grid · SafeRec + WeSwitchPayroll API credential timeline · risk register

Marketing

Landing Page

Consumer-facing site · contractor vs hirer vs agency type cards · take-home comparison calculator · pricing

Handoff

Developer Pack

Complete developer handoff · file inventory · CEST factor weights · decision logic · onboarding checklist

CEST 8-factor scoring model
#FactorWeightInside indicators
1Control22%Client dictates how, when, where work is done
2Substitution20%Worker cannot send a substitute; client must approve
3Mutuality of obligation18%Client obliged to offer work; worker obliged to accept
4Financial risk14%No financial risk; no bad debt; no fixed-price projects
5Equipment8%Client provides all equipment and materials
6Integration8%Worker integrated into client's organisation
7Exclusivity6%Restricted from working for other clients
8Part and parcel4%Worker attends client events, appraisals, named on org chart
Determination logic
score > 65 AND claude = inside AND confidence ≥ 65% → INSIDE (FCSA referral triggered)
score < 35 AND claude = outside AND confidence ≥ 65% → OUTSIDE (SDS issued immediately)
else → BORDERLINE (India QA mandatory · SDS held)

s61P ITEPA 2003 — SDS must be acknowledged within 31 days or liability shifts to hirer
Chase schedule: D7 · D14 · D21 contractor emails · D31 escalates to India QA
Runtime (n8n workflows)
Runtime (document templates)
Runtime (deployment)
🐳Dockerfile — Node 20 Alpine · 4-stage build · non-root nextjs userDone
🚂railway.json — eu-west · app.ir35.law · 2 replicas prodDone
🔑.env.example — Claude · Stripe · Resend · WSP API · SafeRec · SDS_ACK_SECRETKey
Cross-references
WeSwitchPayroll — FCSA umbrella panel · referral fee on every inside/borderline conversion
payroll.law — hirer moves contractor inside → employer PAYE + payroll.law subscription
accounts.law — every contractor PSC needs annual accounts + CT600
employ.law — hirers with inside contractors need ERA 2025-compliant employment contracts
SafeRec — agency API integration for bulk SDS issuance + audit trail
India QA — every BORDERLINE determination reviewed before SDS issued