Completed kitchen extension with island and large sliding doors

How to Choose a Builder in London: Checks, Quotes and Red Flags

By the Golbik GBS team · Blog

Choosing the right builder matters more than almost any other decision in a renovation. A good builder keeps the project safe, on schedule and within budget; the wrong one can cost far more than the price difference between quotes. This checklist covers what to check before you sign.

Key takeaways

  • Check the company, its insurance and independent reviews before inviting quotes.
  • Ask for registrations that cover specialist work: NICEIC or similar for electrics, Gas Safe for gas.
  • Compare itemised written quotes based on the same specification, not just the total.
  • Agree a written contract and stage payments linked to completed work, not large sums upfront.
  • Be wary of cash-only deals, pressure to decide quickly and quotes far below the others.

Before You Ask for Quotes

  • Check the company – a limited company can be looked up on Companies House to confirm its registered address, directors and how long it has traded.
  • Read independent reviews – look for a track record on platforms such as Checkatrade and Google, ideally with recent jobs similar to yours.
  • Ask about insurance – public liability insurance as a minimum, and ask to see the certificate.
  • Check registrations – NICEIC or a similar scheme for electrical work, Gas Safe for any gas work.
  • Ask about waste – builders removing waste should hold a waste carrier registration with the Environment Agency.
Completed kitchen extension with island and large sliding doors
A completed kitchen extension with an island and sliding doors

Questions to Ask Every Builder

QuestionWhy it matters
Who will manage the project day to day?A single point of contact reduces delays and miscommunication
Who handles Building Control and Party Wall notices?Responsibility should be clear before work starts
What is included and excluded in the quote?Exclusions and provisional sums are where costs grow
What is the programme and payment schedule?Stage payments should follow completed work
What certificates will I receive?Electrical, gas and Building Regulations certificates are needed when you sell
Can I see similar projects?Recent work and reviews show quality and reliability

Comparing Quotes

Give every builder the same drawings and specification. Compare itemised quotes line by line, check what is described as a provisional sum, and ask about anything that appears in one quote but not another. The cheapest total is often the one with the most exclusions. Our full refurbishment guide explains what a complete scope of work usually includes.

Contracts and Payments

  • Use a written contract; for larger domestic projects, standard forms such as the JCT contract for homeowners are widely used.
  • Agree stage payments linked to completed work, with a small retention until snagging is finished.
  • Record changes in writing, with the cost agreed before the work is done.
  • Make sure approvals are in place: planning or permitted development, Party Wall agreements and Building Regulations. See planning rules by borough.

Red Flags

  • Cash-only payment or a discount for paying without a receipt.
  • Pressure to sign the same day or to pay most of the price upfront.
  • No business address, company details or written quote.
  • A price far below the other quotes with little detail.
  • Reluctance to provide insurance details, registrations or references.
Kitchen extension with glass roof and herringbone floor
A finished kitchen extension with a glass roof

Frequently Asked Questions

How many quotes should I get?

Three is a sensible number for most projects. Give every builder the same drawings and specification so the quotes can be compared like for like.

How much deposit should I pay a builder?

Avoid paying a large sum upfront. A modest deposit for materials or scheduling may be reasonable, with the rest paid in stages as agreed parts of the work are completed.

How can I check an electrician or gas engineer?

Electricians registered with a competent person scheme such as NICEIC can be checked on the scheme’s register, and gas engineers on the Gas Safe Register. Ask to see the relevant card or registration number.

What are my rights if I sign a contract at home?

For contracts agreed at your home, consumers usually have a 14-day cancellation period. Under the Consumer Rights Act 2015, services must also be carried out with reasonable care and skill.

How We Approach Your Project

Golbik GBS Ltd is a registered company (Companies House 12142749), has been on Checkatrade since 2016 with a rating of 9.8 out of 10 from 130 reviews, and our electrical work is carried out as a NICEIC Domestic Installer. Read our customer recommendations, explore our full refurbishment and extension services, or request a quote.

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