How Do I Compare London Construction Quotes and Choose a Qualified Contractor?

Why do London construction quotes vary so much for the same job?

Quotes vary because the headline total often hides different assumptions about what the contractor will supply, organise and carry away. Your job is not to find the lowest number. Your job is to make each number describe the same job.

Citizens Advice says homeowners should obtain written quotes from at least three traders. It also says a quote should include a fixed total and a breakdown of the work and materials. Flintshire County Council Trading Standards makes the same practical point: separate the cost of work from the cost of materials.

Run a same-job test. Put every quote into one worksheet before discussing who seems cheapest. If one builder includes a task and another does not mention it, mark it as unresolved rather than pretending the two prices are comparable.

This is where cognitive load drops. You are giving each contractor one clean opportunity to describe the same deliverable. The Building Control Partnership specifically recommends a breakdown covering materials, labour, working hours, timeframes, completion date, subcontracting, waste disposal and VAT.

What should be included in a builder's quote for a loft conversion or extension?

A builder's quote should set out a fixed total, a detailed scope and materials breakdown, VAT treatment, its validity period, timing, payment terms and the circumstances in which the price can rise.

Start with the document, not the sales conversation. Citizens Advice says the quote should show separate costs for each material and work element, and explain when the price could increase. That turns a vague promise into a record you can use when a question appears later.

Use the phrase swap below when a quote is light on detail.

Weak request: "Can you make the quote more detailed?"

Stronger request: "Please revise the quote to show the fixed total, work and materials breakdown, VAT, timing, payment stages, subcontracting, waste disposal, exclusions and every item that needs approval before the price changes."

Then check the contractor, not just the paper. Companies House says its Find and update company information service makes public company data available free of charge. The register can show whether a company is active or dissolved, plus filing dates, current and resigned officers, document images, mortgage charges and insolvency information. That does not replace a judgement call, but it gives you a factual starting point.

Ask for insurance confirmation that remains in force during the work, references and recent work you can inspect. Flintshire Trading Standards recommends three references, checking trading history and asking for relevant trade-association certificates. The Building Control Partnership notes that TrustMark displays indicate checking by a government-approved trade association or certification body against specified standards; it also notes that National Federation of Builders members have public-liability insurance and a formal complaints procedure.

Should I accept a fixed-price quote or an estimate?

Accept a fixed-price quote when you need price certainty; use an estimate only when you understand that it is a rough price that can change and have agreed how changes will be handled.

The distinction matters because it changes the conversation before work begins. Flintshire Trading Standards defines an estimate as a rough price that could change, while a quote is an exact price that cannot increase without your agreement. Citizens Advice likewise says a trader cannot raise a written quote simply because their own costs increased after issuing it.

Extra work is the pressure point. If it becomes necessary, Citizens Advice says the trader must tell you and obtain agreement to the additional price before charging more. Use a stop-and-write rule: no added task, substituted material or price change is accepted until the scope and cost are recorded in writing.

Say this: "Please send the proposed variation, the added price and any effect on timing in writing before work continues on that item." That line is calm, specific and hard to misunderstand.

Put payment in the same written agreement. Citizens Advice advises avoiding full upfront payment. Where a deposit is unavoidable for a long project, it recommends aiming for no more than 25% and obtaining a receipt. For larger projects, the Building Control Partnership recommends a written payment schedule and withholding final payment until the work is satisfactory and the building-control completion certificate has been received.

For a homeowner-occupier dealing directly with a contractor on small domestic work, including extensions and alterations, JCT HO/B 2021 is designed for that arrangement. JCT says it uses an agreed lump sum including VAT, payable on completion or through agreed interim payments, and addresses work scope, planning permission, building regulations, party walls, insurance, guarantees, changes and disputes.

Before you choose, run one final drill: take the lowest quote and identify every point it does not state. Send those questions in writing. If the replies still cannot make it comparable with the other quotes, do not reward uncertainty with a signature.