In almost every case, yes. Before any excavation you should establish what services are buried beneath the ground, and a utility survey is the standard way of doing it. UK safe digging guidance, principally the HSE’s HSG47, expects buried services to be located and marked before you break ground, and a PAS 128 utility survey provides exactly that: a detected, mapped record of what is below so you can dig around it rather than into it.
A utility survey is one of the cheapest forms of risk management on a construction project. A single service strike can injure or kill, cut power to a neighbourhood, halt your programme and run to serious cost, and nearly every strike comes down to the same root cause: nobody knew the service was there. A survey removes that excuse before the first machine arrives.
What the guidance expects
There is no single clause that says “thou shalt commission a utility survey”, but the duties point firmly in that direction. The HSE’s guidance HSG47, Avoiding danger from underground services, sets out a safe system of work built on three steps: plans, locate and dig safely. The first two are, in practice, what a utility survey delivers.
Under the Construction (Design and Management) Regulations and general health and safety duties, anyone controlling excavation work has to plan it so that people are not put at risk from buried services. You cannot plan around a hazard you have not identified, which is why locating services in advance is treated as a basic precaution rather than an optional extra. Our guide to avoiding utility strikes under HSG47 walks through that safe system of work step by step.
Why records alone are not enough
The obvious question is whether you can simply pull the statutory plans from the utility companies and skip the survey. Records are a necessary starting point, but they are not a reliable finish.
- Records are often incomplete. Private cables, disused services, and connections made informally over decades frequently never make it onto an official plan.
- Records are often inaccurate. Plans show intended or approximate positions, not verified ones, and services move during their life, get diverted, or were never laid where the drawing says.
- Records have no depth you can trust. Ground levels change, surfaces are resurfaced, and a service that was once at safe depth may now sit far shallower than expected.
A survey resolves these gaps by detecting what is actually in the ground on the day, then reconciling it against the records rather than trusting the paper on its own.
What a survey before excavation gives you
A PAS 128 utility survey uses complementary detection methods to find buried services and produces a coded drawing you can design and dig against.
- Electromagnetic location (EML) finds metallic and conductive services such as power cables and metal pipes, and can trace live cables.
- Ground penetrating radar (GPR) finds non-metallic services that EML cannot, including plastic pipes, ducts and fibre, plus voids.
- A coded CAD drawing records the located services, classified against the PAS 128 quality levels, with a method statement setting out coverage and limitations.
Used together, EML and GPR give far more complete coverage than either alone. You can read more about how radar detection works in our GPR survey guide.
When a survey matters most
Some works carry more risk than others, and the case for a survey grows with the stakes.
| Situation | Why a survey matters |
|---|---|
| Mechanical excavation, trenching or digging | Machines strike services fast and with force; detection lets you locate and hand-dig near them |
| Piling and foundation work | A pile through a live main is catastrophic and unrecoverable |
| Working near high-pressure gas or HV cables | Strikes can be fatal; these often warrant physical verification |
| Congested urban sites | Multiple utilities in a narrow corridor are easy to hit without a map |
| Sites with a long or unknown history | Old and undocumented services are common and rarely recorded |
Even on a modest job, the maths is stark: the cost of a survey is trivial next to the cost, delay and liability of a strike.
Detect, then verify where it counts
A survey is not a guarantee. No detection method finds every service, particularly non-conductive or poorly recorded ones, which is why detection is paired with safe digging practices rather than replacing them. For the highest-risk positions, detection is taken a step further to QL-A verification, physically exposing the service by trial hole or vacuum excavation to confirm exactly where it is before you dig near it.
The sensible pattern for most projects is a layered one: map the whole site by detection at QL-B, then verify the critical points at QL-A. Our guide to PAS 128 quality levels explains how those levels of confidence fit together.
Common questions
Is a utility survey a legal requirement before excavation?
There is no single law naming a utility survey, but health and safety duties require excavation to be planned so people are not endangered by buried services, and the HSE’s HSG47 guidance expects services to be located before digging. In practice a utility survey is how those duties are met, which is why it is treated as a standard precaution rather than an optional one.
Can I just use utility company records instead of a survey?
Records are an essential first step but not a substitute for detection. They are frequently incomplete or inaccurate, often omit private and disused services, and rarely give reliable depths. A survey detects what is actually in the ground and reconciles it against the records, giving a far more dependable picture to dig against.
Will a survey guarantee I will not hit a service?
No survey can guarantee that, because no detection method finds every buried service, especially non-conductive or unrecorded ones. A survey significantly reduces the risk by locating and mapping services in advance, and it is combined with safe digging practices and, at critical points, physical verification to confirm position before excavation.
How far before excavation should the survey be done?
Ideally the survey informs design and planning, so it is best carried out well before works begin, giving time to design foundations and services around what is found and to plan safe digging. On live sites, positions can change, so for high-risk works a fresh check or verification close to the excavation is sensible.
What do I get from the survey?
You receive a coded utility drawing in CAD showing the located services, classified against the PAS 128 quality levels, together with a method statement describing the equipment used, the areas covered and the limitations. It is the record you use to design, plan and dig safely.
If your programme includes digging, trenching, piling or foundation work, locating what is below first protects both people and the schedule. Our underground utility surveys are carried out to PAS 128 across London and the UK, and it is worth pairing this with our PAS 128 quality levels guide so you can specify the right level of confidence for the risk.