How to Choose a Building Contractor in London: A Practical Guide

**Membership of recognised trade bodies:** Reputable building contractors in the UK hold membership of recognised trade bodies that require members to demonstrate competence and maintain professional standards. The most significant for residential building work are:

• •**Checkatrade** — a verified contractor review platform that vets businesses before listing and monitors customer feedback, providing accountability for clients
• •**Google Reviews and social media** — direct client feedback across Google, Facebook, and other platforms providing real-world accountability
• •**Which? Trusted Traders** — a review-based platform that vets businesses before listing and monitors customer feedback

Membership of these bodies does not guarantee excellent work — but it provides a mechanism for accountability and a process for resolving disputes that does not exist with an unaffiliated contractor.

• **Insurance:**
• Before agreeing to any contract, ask the contractor to provide certificates showing:
• •**Public liability insurance** — minimum £2M, ideally £5–10M. This covers damage to your property or third parties caused by the contractor during the works
• •**Employer's liability insurance** — mandatory for any contractor employing staff; covers injury to workers on your site
• •**Professional indemnity insurance** — relevant where the contractor is providing design-and-build services including design advice

A contractor who is reluctant to provide current insurance certificates, or whose certificates are expired, should not be engaged.

**Previous work and references:** Ask to see examples of completed work of a similar type and scale — ideally with a site visit to a previous project where possible (with that client's consent). Ask for client references and follow them up with a direct call rather than relying on written testimonials, which may be curated.

• **Company registration and financial standing:**
• Look up the contractor's company registration number on Companies House. This takes two minutes and shows:
• •How long the company has been trading
• •Whether accounts are up to date (a company repeatedly filing late accounts may be in financial difficulty)
• •Whether there are any insolvency proceedings
• •Who the directors are and whether they have any history of dissolved companies

A newly formed company with a single director and no filed accounts is a higher risk than a long-established limited company with a track record. This does not mean sole traders or newer businesses should be avoided — but the due diligence should be proportionate to the risk.

**Red flags when receiving quotes:**

• •**Unusually low price:** A quote materially lower than others received is not a reason to celebrate — it is a reason to ask why. Either the contractor has missed scope, is buying the job intending to raise costs through 'variations', or is working on margins that will lead to corner-cutting or cash flow problems
• •**Quote with no breakdown:** A single lump-sum figure with no scope or line-item detail makes it impossible to compare quotes fairly or to identify what is and is not included
• •**Request for large upfront payment:** A legitimate contractor does not need a large cash payment before starting work. Standard practice is a modest mobilisation payment (10–20% at most) with staged payments tied to project milestones. A request for 30–50% upfront before a single brick is laid is a serious red flag
• •**Cash only or no invoice:** Refusal to provide a formal invoice or insistence on cash payment (with offers to 'remove the VAT') is a red flag both for tax compliance and for the ability to resolve disputes through normal channels
• •**No written contract offered:** Any contractor unwilling to work under a written contract should be avoided. The reluctance almost always indicates that the contractor wants flexibility to alter price and scope without the accountability a contract creates
• •**Pressure for immediate decision:** A reputable contractor does not need you to decide immediately. Pressure selling ('I can only hold this price for today') is a manipulation tactic

**Green flags when receiving quotes:**

• •Detailed written scope of works that makes clear what is included and excluded
• •Clear programme showing key stages and expected completion
• •Staged payment schedule tied to project milestones
• •References to Building Regulations, structural engineer coordination, and party wall where relevant
• •Willingness to explain the quote and work through any questions
• •Transparency about who will be on site and how the project will be managed day-to-day

**Never start work without a written contract.** This is not bureaucracy for its own sake — the contract is the only enforceable record of what was agreed, and it protects both the client and the contractor.

A proper building contract for London residential work should include:

**Scope of works:** A clear description of what work is to be carried out. A written scope of works or schedule of works is the core document. Vague contracts like 'extension as discussed' create disputes.

**Price:** The agreed contract sum, what it includes, and what is excluded. Where provisional sums are used (for work that cannot be fully priced until the works are underway), these should be clearly identified as provisional.

**Programme:** Expected start date, expected completion date, and any key milestone dates. The contract should address what happens if the programme is extended by events outside the contractor's control (agreed extension of time) vs. contractor delay.

• **Payment schedule:**
• Staged payments tied to project progress, not to arbitrary dates. Typically:
• •10–20% mobilisation on contract execution
• •Stage payments at defined milestones (foundations complete, structure complete, first fix complete, second fix complete, etc.)
• •Final payment (typically 2.5–5% of contract sum) on Completion Certificate issue and snagging sign-off

**Variations:** How changes to the agreed scope are managed — the contract must make clear that no variation to the price or scope is agreed unless it is confirmed in writing by both parties. Oral 'while you're at it' instructions are a major source of dispute.

**Dispute resolution:** A mechanism for resolving disputes without going immediately to court — typically referral to an independent adjudicator or mediation. recognised trade bodies memberships provide additional dispute resolution mechanisms.

**At rcbGroup:** RCB issues a written scope of works and contract before any project begins. This is not optional — it is a core part of how rcbGroup operates and how both parties are protected throughout the project.