How to Choose a Building Contractor in London: Vetting, Checks, and Red Flags 2025

A credible London building contractor should be able to provide — without hesitation — all of the following information. If a contractor cannot or will not provide this information, it is a disqualifying red flag: Company registration information: the company's registered name, Companies House registration number, and registered office address. Verify this independently at beta.companieshouse.gov.uk. Check: How long has the company been registered? Has the company had any previous names (which may indicate a phoenix company — a new company formed after a predecessor became insolvent)? Are there any County Court Judgements (CCJs) against the company (search at Registry Trust)? Public Liability Insurance: minimum £5,000,000 public liability cover (some domestic clients require £10,000,000 for larger projects). Request a copy of the current insurance certificate, not just confirmation that it exists. Check the expiry date and the policy schedule (what activities are insured, what exclusions apply). Employer's Liability Insurance: mandatory for any company with employees. Request a copy of the current certificate. Professional indemnity insurance: if the contractor is also providing design services (design-and-build), professional indemnity insurance is also required. Membership of a recognised trade body or quality scheme: the most credible construction industry bodies for domestic contractors in the UK include: FMB (Federation of Master Builders) — requires members to pass an independent inspection of their work before admission, and offers a free client support service for disputes; TrustMark — a government-endorsed quality scheme for domestic tradespeople; Checkatrade, TrustATrader, Which? Trusted Traders — consumer review platforms with vetting requirements. Membership of a recognised body does not guarantee quality, but it does demonstrate a minimum commitment to professional standards and provides recourse if problems arise. Relevant examples of similar completed projects: request 3-5 examples of similar completed projects (similar size, type, and specification to your project) with the addresses and dates. Follow up by: visiting the completed project addresses (or asking the client references for current photographs of the completed work); contacting the clients directly for references (request 3 direct references you can call or email — not testimonials the contractor has selected and published on their website); checking planning portal records to verify the project was completed as described (extension sizes, dates, and addresses). Financial stability: request the last two years of company accounts from the contractor (publicly available at Companies House for limited companies). Review the accounts for: significant year-on-year growth in turnover (which can indicate a business that is growing faster than its management capacity); significant recent losses (which may indicate financial instability); unusually high director loans (which may indicate extraction of funds from the company in anticipation of a wind-up). A contractor who is financially stable and well-managed is more likely to complete the project and to stand behind their work during the defects liability period.

A proper written building contract is not optional for a London renovation project above the most minor works. Without a written contract, the legal framework governing the relationship between client and contractor defaults to the implied terms of a simple contract for services — which gives the client very limited rights if things go wrong. A proper building contract for a London residential renovation should include at minimum: Specification of works: a clear, detailed description of all the works to be carried out, by reference to the design drawings and specifications. The contract should incorporate the current set of drawings (with their drawing numbers and revision letters) by reference. Contract sum: the total agreed price for the works as described in the specification. Variations procedure: a clear mechanism for agreeing and costing any changes to the scope of works (additions, deletions, or substitutions) — including the agreement that no additional work will be carried out without a written variation instruction and an agreed price or rates basis. Payment schedule: the agreed payment milestones and the amounts due at each milestone. For a domestic project in England, the client has statutory rights under the Housing Grants, Construction and Regeneration Act 1996 (as amended) — including the right to pay by reference to payment notices and the right to withhold payment by issuing a pay less notice before the final date for payment. Practical completion and defects liability: the definition of practical completion, the agreed mechanism for inspecting and listing defects at practical completion (a snagging list), the retention amount (typically 2.5-5% of the contract sum, withheld for a defects liability period — typically 6 or 12 months), and the release of retention at the end of the defects liability period on satisfactory rectification of the defects. Dispute resolution: a clear mechanism for resolving disputes without litigation — typically adjudication (a fast and relatively low-cost statutory process available to all parties to a construction contract in England) and, where the dispute cannot be resolved by adjudication, arbitration or litigation. Recommended contract forms for domestic projects in London: JCT Homeowner Contract — a straightforward, plain English contract suitable for domestic works up to approximately £100,000. JCT Minor Works Contract (MW) — suitable for projects £30,000-£500,000 where an architect is administering the contract. FMB Building Contract — the Federation of Master Builders' own contract form, suitable for domestic projects. NEC4 Short Form — suitable for simple construction projects where a progressive, collaborative contract approach is preferred.

The payment structure in a building contract is one of the most important protections for a domestic client. The wrong payment structure — paying too much too soon — is the primary mechanism by which cowboy contractors extract money from clients before walking off site or becoming insolvent mid-project. A sound payment structure for a London renovation project: Stage payments linked to measurable milestones: payments should be made at defined completion milestones — foundation complete, structure to wall plate, roof watertight, first-fix M&E complete, second-fix and finishes, practical completion. Each milestone payment should be a genuine reflection of the value of work completed to that stage. Retention: a retention amount (typically 2.5-5%) is withheld from each stage payment and released at the end of the defects liability period. This gives the client leverage to ensure the contractor returns to rectify any defects identified after completion. Avoid large upfront payments: a contractor who demands a large deposit before starting work (more than 10-15% of the contract sum as a mobilisation payment) should be treated with caution. The mobilisation payment is justified as a contribution to materials and initial site set-up costs — but a payment more than 10-15% before work starts is an inappropriate transfer of risk to the client. Never pay ahead of completed work stages. VAT on construction services: most building work on an existing residential property is subject to standard rate VAT (20%). However, some categories of work may qualify for reduced rate VAT (5%) — including: conversion of a non-residential property to residential use; renovation of a property that has not been lived in for two years or more; installation of energy-saving materials (but this has changed significantly in recent years). Always clarify the VAT treatment with the contractor before agreeing the contract sum, and check with HMRC or a VAT specialist if the VAT rate is in dispute. Red flags in payment demands: requests for payment in cash (not in the contractor's bank account); requests for payment to a personal account rather than the company account; payment demands before the agreed milestone is complete; resistance to written confirmation of milestone completion before releasing payment; pressure to pay ahead of agreed terms citing cash flow problems.

The following are disqualifying red flags when selecting a building contractor for a London renovation: No written quote: a contractor who provides only a verbal estimate or a one-line email price without a detailed breakdown of the scope of works, the materials included, the exclusions, and the assumptions. No contract: a contractor who resists providing or signing a written contract. No insurance: a contractor who cannot immediately produce copies of current public liability and employer's liability insurance certificates. Cash-only requests: a contractor who requests cash payment, or who asks for payment in advance of agreed milestones. Pressure sales tactics: a contractor who applies pressure to sign quickly (citing other jobs they might take, claiming the price is only valid for a very short period, or offering a large discount for immediate commitment). Evasion of references: a contractor who cannot provide or who evades requests for direct client references from comparable completed projects. Resistance to a proper contract: a contractor who says they never use contracts because they work on trust. Lack of traceable company information: a contractor who cannot provide a Companies House registration number or whose company information cannot be verified online. Very significant underbidding: a contractor whose quote is dramatically lower than all other competitive quotes (more than 25-30% lower) — which may indicate that the contractor has not priced all the scope, plans to use sub-standard materials, or intends to increase the price through variation orders after work starts. VAT evasion: a contractor who offers a lower price for cash payment (which is a mechanism for VAT evasion). Participating in this arrangement creates legal risk for the client as well as the contractor.