Why finding a good builder in London is genuinely hard
London has more construction businesses per capita than almost anywhere in the UK. The London Building Control area alone processes tens of thousands of building regulations applications annually. Yet the number of truly verified, consistently high-quality residential contractors is a fraction of the total market.
The problems are structural. Construction is one of the least regulated industries in the UK. Anyone can legally describe themselves as a builder, general contractor, or project manager without qualifications, insurance, or a track record of completion. Review platforms are widely acknowledged to be gameable. Word of mouth is valuable but limited in a city where most people do not know their neighbours.
Here are the seven steps that will meaningfully reduce your risk.
Step 1: Define your project precisely before making contact
Before you approach a single builder, you need to know what you are asking them to price. A vague brief ("we want to extend at the back") will produce vague — and incomparable — quotes.
At minimum, clarify:
- The type of project (rear extension, loft conversion, refurbishment, etc.)
- Approximate size and scope
- Whether you have planning permission or drawings yet
- Your intended start date and budget range
- Whether you want a design-and-build service or build-only
Builders who quote without this information are giving you a number that means very little.
Step 2: Check company registration and trading history
Every legitimate building company in the UK should be registered at Companies House. Search for the company name or director's name at companieshouse.gov.uk and check:
- How long the company has been registered
- Whether accounts have been filed consistently
- Whether the company is active or has been dissolved and reformed
- Whether the director has a history of dissolved companies
A company that has been trading for less than two years under its current name, or whose director has a trail of dissolved companies, warrants extra scrutiny.
Step 3: Verify their insurance — not just that they have it
Ask for a copy of their public liability insurance certificate. The minimum acceptable limit for a London residential project is £2 million, though £5–10 million is more appropriate for larger projects.
Check:
- That the policy is current (not expired)
- That the insured trading name matches the company you are dealing with
- That the policy covers the type of work you are commissioning
Employers' liability insurance is legally required if the contractor employs staff directly. Ask for this too.
Step 4: Ask for references from similar recent projects — and call them
Testimonials on a website or portfolio photos tell you very little. What matters is speaking directly to someone who commissioned similar work in the last 12–24 months.
Ask the reference:
- Did the project complete on budget and on time?
- How was communication during the project?
- Were there unexpected additional costs? How were they handled?
- Would you use them again?
A builder who cannot provide references from recent comparable projects should be treated with caution.
Step 5: Get at least three detailed, itemised quotes
Do not accept a single-line quote ("extension, supply and fit, £65,000"). Require an itemised breakdown that allows you to compare like for like, including:
- Demolition and enabling works
- Structural works and steelwork
- Roofing
- Glazing and external doors
- First-fix electrics and plumbing
- Insulation and drylining
- Second-fix (and whether materials are included or client-supplied)
- Provisional sums for items to be confirmed
If two quotes are far apart, the difference is almost always in what is included — not in who is overcharging.
Step 6: Check CDM compliance awareness
Under the Construction (Design and Management) Regulations 2015, any domestic project involving more than one contractor working at the same time triggers duties for the homeowner as Client. A reputable builder should know what these are and be able to advise you on appointing a Principal Contractor.
If a builder looks blank when you mention CDM 2015, or tells you it does not apply to domestic work (it does), that is a warning sign about their professional standards.
Step 7: Use a verified contractor platform
Checkatrade, Rated People, and similar platforms aggregate reviews but do not verify compliance data. For a London extension or refurbishment project worth £50,000+, look for platforms that verify:
- Companies House registration
- Public liability insurance currency
- HSE notifiable project history
- Director trading history
Dwellinger's Builder Score™ is a 0–1000 composite rating built from this verified data — giving you a compliance-grounded assessment alongside customer reviews.
Red flags to avoid
- Builder asks for large cash upfront (more than 10–15% deposit before work starts)
- No written contract offered
- Unwilling to provide insurance certificate or Companies House number
- Pressure to start immediately or discount expires today
- No professional fee for site visit or estimate (may indicate low-quality leads)
- Refuses to provide references
The bottom line
Finding a trustworthy builder in London requires more due diligence than most homeowners expect. The market is large, loosely regulated, and full of operators who look credible on the surface. The seven steps above will not guarantee a perfect project — but they will significantly reduce the probability of a bad one.