How to check a contractor before you sign: seven checks that take an hour

None of these checks require a solicitor or a quantity surveyor. They require a company number, twenty minutes on Companies House and a willingness to ask four slightly awkward questions. The contractors worth hiring expect them.

The stakes are real. The Insolvency Service recorded 3,866 construction company insolvencies in England and Wales in the 12 months to August 2026, more than any other sector, although 2% fewer than a year earlier. Output is soft too: the ONS has construction down 0.5% in the three months to July 2026. A contractor who is stretched is a risk to your programme and your budget, so it is worth knowing who you are dealing with. This guide is written for clients choosing a building contractor, and it uses plain terms so you can run the checks yourself.

How do you choose a building contractor?

Start with the job, not the price. Write down what you need built, where, by when and what must keep working while it is built. Then ask each contractor the same questions in the same order, so the answers can be compared. The seven checks below are that list. A good contractor will answer them in specifics and send documents. A poor one will answer in general terms and say the paperwork is on its way.

What the law expects of you as the client

Under the Construction (Design and Management) Regulations 2015, known as CDM, a commercial client has duties of its own. You must make suitable arrangements for managing the project, give designers and contractors the information they need about the site, and allow enough time and money for the work to be done safely. Where more than one contractor will be involved, you must appoint a principal designer and a principal contractor in writing. The HSE guidance for commercial clients sets this out.

The principal contractor plans, manages and coordinates the construction phase, including preparing the construction phase plan before work starts. If you do not make the appointments, the regulations say those duties fall to you as the client. Most clients would rather hand them to someone who does this every week. Our write-up of what a principal contractor does shows the role on a live factory site.

A project is notifiable to the HSE if the work lasts more than 30 working days with more than 20 workers on site at once, or exceeds 500 person-days. Many commercial builds clear that bar, so ask the contractor early whether yours will.

The seven checks before you sign

• Ask who the principal contractor is, in writing. The contract should name the principal contractor and principal designer. If the answer is vague, so will be the site management.
• Ask for the insurance certificates. Employers' liability cover is a legal requirement with a minimum of £5 million. Ask also for public liability and contract works cover, check the limits suit the size of your job, and check the certificates are in date.
• Read the accounts. Companies House shows filed accounts, the filing history and any charges registered against the company. Late filings, shrinking net assets or a run of new charges are all worth asking about.
• Ask to see something finished. A contractor who has built a similar building should be glad to show you one, and put you in touch with the client. Ask that client about the end of the job, not the start: snagging, handover and what happened when something went wrong.
• Find out who does the work. More below.
• Read what the price leaves out. Groundworks, utilities connections, planning fees, building control and drainage are the usual gaps. Ask how long the price is valid too, because steel is moving quickly this year. We cover that in our piece on steel prices.
• Ask for the construction phase plan and a programme. You should see how deliveries, access and site safety will be handled, and a programme with named stages, not a single finish date.

Which accreditations should a contractor hold?

Accreditations are third parties checking a contractor so you do not have to start from nothing. They do not replace your own checks, but a contractor with none of them is asking you to take more on trust. These are the ones you will meet most often on commercial and industrial work.

• Constructionline: a register of pre-qualified suppliers, with tiers. Gold is a higher level than the entry tier. Ask for the current certificate and check it against the register.
• SafeContractor: a health and safety assessment scheme. It looks at policies, risk assessments and training, and clients often ask for it in pre-qualification questionnaires.
• UKCA or CE marking: for structural steel, the steelwork delivered to a site in Great Britain must be UKCA or CE marked to BS EN 1090-1. Ask the fabricator for the certificate and the Execution Class it covers. Our guide to in-house steel fabrication lists the three documents to ask for.
• UKAS-accredited SCCS certification: the Steel Construction Certification Scheme covers structural steelwork, and UKAS is the national accreditation body that checks the certifying body.

A certificate is only useful if it is current and covers the work you want done, so read the scope and the expiry date, not just the logo.

Who actually does the work

Subcontracting is normal, and for groundworks or specialist services it is often the right call. The question to ask is about the parts that set your programme and your quality. On a steel framed building that means the frame: who designs it, who fabricates it, and who puts it up.

When those are three separate firms, you have three sets of deadlines and a lot of places for things to slip between. When one company does all three, there is one programme and one point of responsibility. At MSB we fabricate the steelwork in our own workshop and our own site team erects it, which keeps the programme in one set of hands. Not every client needs that, but every client should know which model they are buying.

What should the price include?

Two quotes that differ by a third are rarely for the same building. Before you compare totals, check that each one states the span, height and specification it has priced, what is assumed about the ground, whether groundworks and the floor slab are in or out, what cladding and doors are included, who fabricates and who erects, and how long the price is held. Anything left blank is a cost that will turn up later. Our steel frame building cost guide shows the layers a price is built from, and our warehouse cost guide does the same for a warehouse.

Red flags to watch for

Some signs deserve a second look. A price far below the others, with no explanation of what has been left out. Insurance certificates that are late or expired. Accounts filed late or not at all. No named principal contractor, or a reluctance to put the appointment in writing. No reference you can phone. A programme that is a single completion date. None of these proves a contractor is poor, but each is a reason to ask more questions before you sign, not after.

How we look at it

We would rather you asked these questions of us than took our word for it. We hold Constructionline Gold and SafeContractor accreditation, UKCA marking and UKAS-accredited SCCS certification for structural steelwork, and we send current certificates on request. Those are the documents to ask any contractor for. A recent example is our work for Magna Specialist Confectioners in Telford, where we are principal contractor on a turnkey extension to a working food factory. If you want to talk through your own project and what a sensible set of appointments looks like, our design and build team can take you through it, and our steel framed buildings page shows what we deliver.

Next step

Send us your brief and your site through our contact page, and ask us for the documents above. We will send them with an indicative range and a note of what it includes.

Questions we get asked

What is the difference between a main contractor and a principal contractor?

A main contractor is the firm you contract with to deliver the job. A principal contractor is a CDM role: the contractor appointed in writing to plan, manage and coordinate health and safety during the construction phase. On most commercial jobs they are the same company, but the appointment still has to be made.

What is the difference between a principal contractor and a subcontractor?

The principal contractor controls the construction phase and is responsible for how the site is run. Subcontractors carry out parts of the work under that control and must follow the construction phase plan.

Who appoints the principal contractor?

The client. If more than one contractor will work on the project, the client must appoint a principal designer and a principal contractor in writing. If the client does not, the client takes on their duties.

What insurance should a building contractor have?

Employers' liability insurance is a legal requirement, with a minimum cover of £5 million. Most clients also ask for public liability and contract works insurance, with limits that match the size and risk of the job. Always ask to see the current certificates.

How do I check a contractor is financially sound?

Read their filed accounts and filing history at Companies House, and look for late filings, shrinking net assets or new charges against the company. Ask how they are funding your job and what happens to your payments if they get into difficulty.

What accreditations should a building contractor hold?

Common ones are Constructionline and SafeContractor, plus certification relevant to the work, such as UKCA marking and Steel Construction Certification Scheme certification for structural steelwork. Ask for current certificates and read what they cover.

How long does it take to check a contractor properly?

About an hour for the paperwork if the contractor sends it promptly, plus time to phone a reference and visit a finished job. It is time well spent before a contract worth hundreds of thousands of pounds.