How to actually assess subcontractor competence, not just collect certificates

Before appointing a subcontractor, CDM 2015 places an explicit duty on the principal contractor to be satisfied that they have the skills, knowledge, experience and organisational capability to carry out the work safely. That's a genuine judgement to make, not a checklist to complete.

Beyond the paperwork

Certificates and accreditations — including CHAS, Constructionline or another SSIP scheme — are useful evidence, but they're not the whole picture. A genuine competence assessment also looks at training records specific to the actual task, a track record on comparable work, and the quality of the subcontractor's own RAMS for the job in question.

What "organisational capability" actually means

This is the part of the CDM wording that gets skipped over most, but it matters — competence isn't just about whether the individuals doing the work are skilled, it's about whether the organisation behind them has the systems to support that work safely. Does the subcontractor's business have a genuine process for supervising less experienced workers? Do they have their own procedure for reporting near misses back up the chain? A single highly skilled tradesperson working for a subcontractor with no real supervisory structure is a different risk profile to the same tradesperson working for a business that actively manages how its people work.

A worked example

Take a groundworks subcontractor bidding for excavation work near a live services corridor. Their CHAS accreditation confirms a baseline of health and safety management. Their RAMS for the job references the specific utility search that's been done for that site, not a generic "check for services before digging" line. Their track record includes comparable work — not just "groundworks experience" broadly, but excavation near live services specifically. And their supervisor on site has the authority and training to stop work if something unexpected turns up. Each of those is a separate piece of evidence; together, they add up to a genuine basis for being satisfied. Any one of them missing doesn't automatically mean the subcontractor isn't competent, but it's a gap worth asking about before signing off, not after.

Labour-only and agency workers

Competence assessment gets harder, not easier, once labour-only gangs or agency-supplied workers are involved, because the individuals actually on site may not be the same people whose track record and training records were reviewed at the point the subcontractor was appointed. It's worth having a clear expectation with any labour-only subcontractor about how new individuals joining the gang get inducted and checked, rather than assuming the original competence assessment automatically covers whoever turns up under that subcontractor's name in future weeks.

Why this matters beyond the initial appointment

Competence assessment isn't a one-off gate at appointment either — it's worth revisiting for higher-risk work even with an established subcontractor, since past reliability on routine tasks doesn't automatically extend to a genuinely different type of work. A groundworks subcontractor who's done reliable, routine excavation work for months isn't automatically competent for excavation near a live services corridor just because the company name is the same — that's a materially different risk, and worth a fresh look.

How to actually have the conversation

Much of a genuine competence assessment happens in conversation, not paperwork review — asking a subcontractor's supervisor to walk through how they'd actually approach a specific task, rather than just checking their documents are in order. Someone who genuinely understands the work can usually describe, in their own words, what could go wrong and how they'd catch it early; someone reciting generic safety language without being able to get specific about the actual task is telling you something too, even if their paperwork looks fine. This kind of conversation takes a few minutes and tends to reveal far more than another read-through of a certificate.

Documenting the judgement, not just the inputs

It's worth recording not just what evidence was reviewed — the certificates, the RAMS, the track record — but the actual judgement made and why. "Reviewed CHAS certificate, RAMS, and prior work on comparable excavation near services; satisfied competent for this task" is a genuine record of a decision. A folder of certificates with no accompanying note of what was actually concluded from them isn't really evidence that a judgement was made at all — it's evidence that documents were collected, which CDM 2015 asks for something more than.

When to say no

The point of a genuine competence assessment is that it has to be able to produce a genuine "no" sometimes, otherwise it isn't really an assessment. If every subcontractor who applies ends up being judged competent regardless of what the review turns up, the process has become a formality rather than a filter. Saying no to a subcontractor — particularly one who's already been provisionally lined up for the work, with a schedule built around them — is uncomfortable, but it's the moment the whole assessment process either means something or doesn't.

Common mistakes

• –Treating a current SSIP accreditation as sufficient on its own, without looking at task-specific evidence
• –Not distinguishing between a subcontractor's general track record and their track record on the specific type of work being assessed
• –Assuming the individuals on site match the profile reviewed when the subcontractor company was first appointed
• –Skipping a fresh competence look when a trusted subcontractor moves into a higher-risk phase of the same project
• –Not checking that a subcontractor's supervisory structure genuinely functions on site, not just on paper
• –Collecting evidence without recording the actual judgement reached from it