What is a PSC tree and when do I need to walk it?

A PSC tree is the graph you get when you walk Companies House's Persons with Significant Control records recursively: starting from a UK company, you find each PSC (an individual or another corporate), and for any corporate-PSC you walk into its own PSC list, repeating up to a maximum depth.

UK regulated firms walk the PSC tree under MLR-2017 reg 5(1)(a) to identify Ultimate Beneficial Owners (UBOs). The regulation defines a UBO as any individual with >=25% effective ownership or control. To compute that through layered structures, you multiply the stake bands at each level: HoldCo owns 50% of OpCo; an individual owns 75% of HoldCo; effective stake of the individual in OpCo is 50% × 75% = 37.5%. That's >=25%, so the individual is a UBO. The lower-bound aggregation rule comes from the Companies House guidance + reg 5(1)(c) covers control-natures (right-to-appoint-and-remove-directors, significant influence) that qualify regardless of share %.

When to walk the tree:

- **AML / KYB onboarding** of any UK corporate counterparty under MLR-2017. - **Letting agents** dealing with corporate landlords (LSAG-2025 §B). - **Conveyancers** dealing with corporate buyer or seller. - **Banks** opening corporate accounts.

Typical depth: 5 levels covers >99% of UK structures cleanly. The Stratum CH Watch API at /v1/ch/companies/{number}/psc-tree?depth=5 walks the tree, computes UBOs with lower-bound aggregation, and screens each UBO against sanctions + PEP + adverse media in one call. Cycle detection + non-UK-leaf flagging are built in.

Source: Companies House PSC Guidance

Last updated 2026-05-06.