The builder you choose for a London home project has more impact on the outcome than almost any other decision. The right contractor turns an ambitious plan into a successful project. The wrong one costs you money, time, and significant stress. This checklist covers everything you should verify before committing.
Step 1: Establish What You Actually Need
Before approaching any contractor, be clear on the scope. At minimum, know:
- What type of project it is (extension, loft conversion, refurbishment, structural alteration)
- Whether you have architectural drawings (and if so, what stage they are at)
- Your target start date and budget range
- Whether planning permission has been obtained
Contractors quote more accurately — and take your project more seriously — when you can provide clear information rather than asking for a price based on a verbal description.
Step 2: Source Candidates Responsibly
Good sources:
- Direct recommendation from friends, family, or neighbours who have used the contractor recently for a similar project
- Architect referral (your architect knows which contractors in London actually deliver their designs)
- Trade association directories: Association of Master Tradesmen and other recognised industry bodies
- Local Facebook groups and community platforms (Nextdoor) — read critically, but genuine local recommendations from people you can follow up with are useful
Treat with caution:
- Unsolicited callers or door knockers
- Contractors who appear suddenly with a very cheap price for "work in the area"
- Online directories without independently verified reviews
Step 3: Verify Insurance
Before any contractor visits your site, confirm they hold:
- Public Liability Insurance: Minimum £2 million (most London contractors carry £5 million). This covers damage to your property or injuries to third parties caused by their work.
- Employer's Liability Insurance: Required by law if they employ any staff (even casual labour). Minimum £5 million.
- Professional Indemnity Insurance: If they are also providing design or professional advice as part of the service.
Ask for a copy of the certificate. Call the insurer to confirm it is current if there is any doubt.
Step 4: Check Trade Memberships and Accreditations
Trade memberships do not guarantee quality, but they do indicate that a contractor has submitted to some level of external assessment:
- Recognised trade bodies: Members are vetted on quality, financial standing, and customer service. Independent dispute resolution available.
- Quality scheme registration: Government-endorsed quality schemes require third-party inspection.
- Client review platforms: Independently verified reviews. Read critically — look at volume, recency, and detail, not just the star rating.
- NICEIC / NAPIT: For electrical contractors. Confirms Part P competence and authorisation to self-certify electrical work.
- Gas Safe Register: For gas engineers. Verify the individual engineer's registration at gassaferegister.co.uk — the company registration is not sufficient.
Step 5: See Completed Work
Ask to visit a completed project similar to yours. A reputable London contractor should be able to arrange this — former clients who are happy with the work will generally agree to a brief visit.
During the visit:
- Look at the quality of visible finishes — plasterwork, paint, tiling, woodwork
- Ask the homeowner how the contractor communicated during the project
- Ask whether the project finished on time and on budget
- Ask whether they would use the contractor again
Step 6: Evaluate the Quotation
A quotation should be:
- In writing
- Itemised (not a single lump sum)
- Clear about what is included and what is excluded
- Explicit about the basis of the price (fixed price, or cost-plus/provisional sums)
- Clear about material responsibilities (what the contractor supplies vs what the client supplies)
- Accompanied by a proposed programme
Red flags in quotations:
- A single total price with no breakdown
- No mention of exclusions or assumptions
- Materials described vaguely as "as required"
- No mention of Building Regulations, structural engineer, or other professionals
- An unusually low price with no explanation
Step 7: Assess Communication
The quality of a contractor's communication before they start work is usually a good predictor of how they will communicate during the project.
Ask yourself:
- Did they respond promptly to your initial enquiry?
- Did they arrive on time for the site visit?
- Did their quotation arrive when they said it would?
- Do they answer questions clearly and completely?
- Do they seem to understand the project?
Step 8: Understand the Contract
Never start work without a written contract. At minimum, the contract should specify:
- Scope of works
- Start date and completion date
- Payment schedule (stage payments tied to work completion, not arbitrary calendar dates)
- Variation procedure (how changes are agreed and priced)
- Dispute resolution process
- Retention (typically 2.5–5% held back for 6–12 months after completion to cover defects)
- Insurance obligations
Standard contracts for residential works include JCT Homeowner Contracts and plain-English alternatives. Avoid contractors who refuse to sign a contract or want to work from a simple letter or verbal agreement only.
Step 9: Check for References and Previous Disputes
Before signing, ask for references from three recent comparable projects. Call them. Ask specifically about:
- Programme adherence
- Budget adherence
- Communication quality
- How disputes or problems were handled
- Whether they would recommend the contractor without reservation
rcbGroup
rcbGroup holds 10/10 from 117+ verified Checkatrade reviews, carries full insurance, and operates under written contracts for every project. We welcome reference requests and site visits to completed projects. Contact us to discuss your project.