TL;DR

Supervision, Direction, and Control (SDC) is the UK HMRC test used to assess employment status for tax purposes, particularly in the context of IR35 and the off-payroll working rules. If a client supervises how a worker does their job, directs what they do, or controls when and where they work, the arrangement looks like employment regardless of what the contract says. SDC is the most operationally significant test in UK contractor compliance.

The Three Components of SDC

SDC is not one test but three separate questions that HMRC applies to the working relationship. Each element can independently indicate employment. All three together constitute strong evidence that the worker is, in substance, an employee.

Supervision means someone checking that work is done correctly and to a required standard, or correcting errors as they occur. A contractor who has their code reviewed line-by-line by a client manager, or whose deliverables are routinely checked and amended by the client, is likely subject to supervision in the SDC sense.

Direction means the client telling the worker how to do their job, not just what outcome to achieve. A contractor told to use specific methodologies, attend particular meetings, or follow defined processes is being directed. The distinction matters: specifying an output is not direction; specifying the method is.

Control means the client determining when, where, and how the worker provides their services. Fixed hours, a requirement to work on-site, and restrictions on working for other clients simultaneously all point toward control. A contractor who sets their own hours, works from their own premises, and is free to work for multiple clients simultaneously has weaker control indicators.

HMRC's guidance acknowledges that these elements can exist on a spectrum. A contractor may have some direction without the full weight of SDC. What matters is the overall picture and which party has the right to supervise, direct, and control — not whether they exercise that right day to day.

Why It Matters for Recruitment

SDC is one of the most consequential compliance tests recruiters encounter, because getting it wrong creates tax liability for the client and potentially the agency. Since the 2021 IR35 reform extended to medium and large private sector clients, the end client is responsible for determining employment status. The fee-payer — usually the agency — is liable for unpaid PAYE and NICs if the determination is wrong.

This means recruitment agencies need to understand SDC not just academically but in terms of how it affects the roles they fill. A contract that is drafted to look outside IR35 but describes a working arrangement with high SDC will be challenged by HMRC. The contract must reflect reality, and the working practices must support the contract.

For hiring managers, SDC awareness shapes how they structure contractor engagements. Keeping contractors at arms length from day-to-day management, paying for outcomes rather than time, and allowing contractors to substitute colleagues where possible all reduce SDC exposure. Many clients struggle to maintain genuine outside-IR35 arrangements in practice because their default management style involves directing and supervising all workers, regardless of status.

In Practice

A software development agency places a senior developer at a bank as an outside-IR35 contractor. The contract specifies deliverables, not hours. In practice, the bank's IT manager emails daily task lists, reviews every pull request, and requires the contractor to be at the office by 9am. HMRC audits the arrangement. The actual working practices — daily direction, constant supervision, fixed hours — demonstrate SDC. HMRC deems the contractor inside IR35. The bank, as the client, is liable for PAYE and employer NICs on the contractor's deemed salary for the duration of the engagement. The agency faces questions about its Status Determination Statement.

Key Facts