Choosing a construction company in London is one of the biggest decisions a homeowner can make. Get it right and your project comes in on time, on budget, and to the standard you wanted. Get it wrong and you're looking at delays, disputes, half-finished work, and — in the worst case — a building that doesn't meet regulations.
This guide covers what to look for in London construction companies, the questions to ask before signing a contract, and the eight red flags that tell you to walk away.
1. Check insurance and credentials before anything else
Any construction company in the UK should hold public liability insurance (typically £2-5 million cover) and contractor's all-risks insurance for the works themselves. If they can't show you the certificates, you're done — no further conversation needed.
Beyond insurance, look for credentials that match the work type:
- Federation of Master Builders (FMB) — membership requires references, inspections, and a code of practice
- TrustMark — government-endorsed quality scheme
- for electrical work
- Gas Safe Register for any gas work
- FENSA / CERTASS for windows and doors
For larger projects involving listed buildings or conservation areas, ask whether the company has worked in your specific local authority before. London boroughs have wildly different planning processes — experience matters.
2. Look at the right kind of references
Every London construction company will give you references. The trick is asking for the right ones. Don't just ask "can I see some recent work?" — ask:
- "Can I see a project that didn't go smoothly?" (How they handled it tells you everything)
- "Can I speak to a client whose project finished 12+ months ago?" (Tests the durability of the work)
- "Can I see a project similar to mine in scale?"
If they only show you their best showpiece projects from years ago, that's a yellow flag. A confident company will happily walk you through recent, similar work.
3. Demand transparent, itemised quotes
A trustworthy construction company in London will give you a written, itemised quote — labour, materials, sub-contracted trades, contingency, VAT — all broken out separately. If a quote arrives as a single round number ("£45,000 to do the extension") with no breakdown, that's a problem. It usually means one of two things:
- They haven't actually priced the job properly and will "discover" extras later
- The number is padded to bury margin you can't see
Cheap quotes are equally suspicious. If three companies quote £40-45k for the same job and one quotes £28k, the cheap one is either dropping quality or planning to add costs later. Walk away.
4. Understand who's actually doing the work
Many "construction companies" in London are essentially project managers who subcontract every trade — plumbing, electrical, plastering, tiling — to different firms. That's not inherently bad, but you need to know:
- Are the tradespeople employed directly or sub-contracted?
- If sub-contracted, are they insured and certified?
- Who's responsible for snagging when trades blame each other?
Companies with in-house teams across multiple trades (general building, electrical, plumbing, plastering) tend to deliver more consistently and have fewer "this isn't my problem" arguments mid-project.
5. Get a clear contract, payment schedule, and timeline
Verbal agreements with a handshake might still happen in the building trade, but they're a terrible idea for any project over £10,000. Before work starts you should have:
- A written contract — JCT short-form is standard for residential
- A payment schedule tied to milestones (not dates)
- A start date and a target completion date
- A liquidated damages clause if completion drags
- A snagging period (typically 2-4 weeks after handover)
- A retention amount (usually 5%) held back until snags are fixed
Never pay more than 10-15% upfront. A construction company that demands 50% before work starts is either cash-flow troubled or planning to ghost you.
The 8 red flags that tell you to walk away
If you spot any of these, find another company:
- No insurance documentation when asked
- Pressure to sign immediately ("price is only valid this week")
- Cash-only payment requests or refusal to issue VAT invoices
- Vague quotes with no itemised breakdown
- Demanding more than 25% upfront
- No physical business address or only a mobile number
- Bad-mouthing other London builders unprompted
- Won't put anything in writing beyond a one-page quote
What to ask in your first meeting
Before signing with any London construction company, ask:
- How many projects of this scale do you complete per year?
- Who'll be my day-to-day point of contact?
- What's your snagging and aftercare process?
- Will you handle Building Regs sign-off and party wall agreements?
- What's your guarantee period on workmanship?
- Can I see a sample contract before I commit?
Their answers will tell you more than any glossy brochure.
Final thought
The right construction company in London is one that takes your project seriously enough to put everything in writing, transparent enough to itemise the quote, and confident enough to show you projects that didn't go perfectly alongside the showpiece work. Trust is built on transparency — anything less is a gamble.
TrustBuilt Projects has been delivering construction and renovation work across London. Every project comes with a single point of contact from first call to final handover. Book a free, no-obligation site visit to discuss your project.