How to Choose a Builder in London: Vetting, Contracts, Red Flags and What Good Looks Like

Personal recommendations: the highest-quality source of leads. Ask neighbours who have done similar work on similar properties. Ask your architect or structural engineer — they work with builders regularly and have direct experience of quality and reliability. Ask your estate agent, who sees the results of building work on similar properties.

Trade directories and accreditation bodies: the recognised trade body (recognised trade body) and NFRC (for roofing) maintain registers of member companies. Trading Standards-backed schemes such as recognised quality schemeoffer an additional layer of accountability. independent client reviews and Rated People aggregate reviews — useful as a signal but less reliable than direct personal recommendations.

Planning applications: nearby planning applications for similar work (loft conversions, extensions) can be found on your council's planning portal. The applicant is often the homeowner who had the work done — you can knock on doors or post through letterboxes to ask about their builder.

Company registration: check Companies House (companieshouse.gov.uk) if the builder operates as a limited company. Note the date of incorporation, the number of directors, and any previous dissolved companies. A company incorporated very recently for a project, or a director with a history of dissolved companies, warrants further scrutiny.

Insurance: any builder working on your property must have public liability insurance (minimum £1 million, preferably £2 to £5 million) and employer's liability insurance (mandatory for any company with employees). Request a copy of the insurance certificate, not just a verbal assurance.

VAT registration: for any project above approximately £40,000 to £60,000, you should expect a VAT-registered contractor. Cash-in-hand offers from unregistered traders on larger projects are a warning sign — they cannot issue VAT invoices if needed for mortgage or insurance purposes, and the arrangement carries legal risk for the client.

References and recent work: request at least two references from recent comparable projects in London. Visit the sites if possible. Speak to the clients directly, not via an email introduction that the builder filters. Ask: did the project finish on time? Was the final cost close to the quoted price? Were snags addressed promptly? Would you use them again?

Professional memberships: membership of the a recognised trade body, Constructionline, or similar bodies is a positive signal (it means the company has been vetted to a standard), not a guarantee of quality. The recognised quality schemescheme requires companies to commit to a code of practice and allows disputes to be escalated.

Provide identical information to all builders quoting (a scope of works, drawings if available, specification of finishes) and ask for a fully itemised quote. Then ask:

• What is your proposed programme for this project?
• Who will be on site day-to-day — employed staff, subcontractors, or a mix?
• Who is my point of contact for day-to-day questions?
• Can you start on the date we need?
• What is your payment schedule?
• What is your process for managing variations?
• Have you done similar work in London before? Can I visit one of those sites or speak to those clients?

A verbal agreement is not adequate for any significant building project. At minimum, the contract should include:

• Exact scope of works
• Contract sum or pricing basis (fixed price, schedule of rates, or cost-plus)
• Payment schedule
• Programme (start and target completion)
• What counts as a variation and how variations are priced
• Defects liability period (typically 6 to 12 months after practical completion)
• How disputes are resolved (the JCT adjudication procedure is included in standard forms)

The JCT Building Contract for a Homeowner (JCT HOM) is a simple, fair, and widely recognised form of contract suitable for most residential projects. The recognised trade body also produces a home-improvement contract for their members. A solicitor's letter of instruction is overkill for a small project but a complete absence of written agreement is unacceptable for any project above a few thousand pounds.

• Requires a large deposit (more than 25 to 30 per cent) before work starts
• Cannot provide proof of insurance on request
• Asks for cash payment or refuses to provide a VAT invoice (on larger projects)
• Gives a very low price without being able to justify it against the scope
• Cannot give a realistic programme or start date
• Refuses to provide references or visits to recent work
• Communicates primarily through unofficial channels and avoids putting anything in writing
• Has multiple negative online reviews referencing the same type of problem (poor communication, unfinished work, disappearing after payment)

A good builder:

• Responds promptly to initial contact and arrives on time for site meetings
• Provides a clear, itemised written quote that specifically includes and excludes items
• Can provide a programme broken down by stage
• Has recent client references who are genuinely satisfied and can be contacted directly
• Uses a written contract (or accepts one you provide)
• Maintains clear communication throughout the project
• Completes snagging promptly after handover

The best builders in London are typically not available at short notice — a builder who can start your project next week when you need it to start in three months is either a warning sign or a rare exception.