London has excellent builders and it has expensive lessons. The difference between the two outcomes is almost never talent — it's paperwork. A verified company, a properly priced schedule, a written contract and a payment structure tied to completed work removes about 90% of the risk before anyone lifts a shovel.
Step one: verify the company, not the person
A friendly quote in your kitchen tells you nothing. Ten minutes of checks tells you almost everything. This is exactly the process behind our KYB verification.
- 1
Companies House
5 minutesConfirm the company exists, its incorporation date, registered address and directors. Look for a pattern of dissolved companies at the same address with the same director — the phoenix pattern is the clearest warning sign in the industry.
- 2
Insurance certificates
Ask for PDFsPublic liability of at least £2m, employer's liability of £5m if they have employees, and — for design-and-build work — professional indemnity. Check the policy dates cover your programme, and that the insured name matches the company on your contract.
- 3
Two completed London projects
Non-negotiableSimilar value, similar type, finished in the last 24 months. Ask to visit one and speak to the owner without the builder present. The question to ask: 'what went wrong, and how did they handle it?' Every project has something.
- 4
Financial sanity check
10 minutesLook at filed accounts. A company turning over £400k should not be taking a £250k project without a clear cash position. Overtrading is how builders disappear mid-project with your deposit funding someone else's job.
- 5
The people who will actually be on site
Before signingAsk who the site manager is, whether trades are employed or subcontracted, and how many concurrent projects they're running. Three or fewer per manager is healthy in London; six is a red flag.
Step two: compare like for like
The most dangerous quote is the cheapest one, because it's usually cheapest for a reason you can't see. Insist on an elemental priced schedule — the same format our instant quote produces — so you can compare line by line.
| Element | Proper quote | Risky quote |
|---|---|---|
| Structure | Elemental schedule A–J with quantities and rates | One page, one number |
| Provisional sums | Named, with a stated allowance | Absent — becomes a variation later |
| Exclusions | Explicit list (kitchen supply, landscaping, decoration) | Vague or missing |
| Programme | Start date, duration, stage dates | 'About four months' |
| Payments | Stage payments tied to completed work | Weekly or monthly regardless of progress |
| Variations | Written process with a labour and mark-up rate card | Verbal, priced after the fact |
| VAT | Stated separately and clearly | Ambiguous or 'cash price' |
No instruction, no variation. Nothing gets built that isn't written down and priced first.
— The line that saves the most money in construction
Step three: use a real contract
| Contract | Use when | Notes |
|---|---|---|
| JCT Home Owner Contract | Projects up to roughly £100k, straightforward scope | Plain English, no contract administrator needed |
| JCT Minor Works Building Contract | £100k–£500k, architect involved | The London standard for extensions; provides for variations, extensions of time and retention |
| JCT Intermediate | Complex or phased whole-house works | Heavier administration; usually architect-run |
| FMB / trade body contract | Small works, trusted contractor | Better than nothing, weaker on dispute mechanics |
| No written contract | Never | Your only remedy becomes the county court |
Step four: structure the payments properly
Payments should always lag the work, never lead it. A schedule where each release is triggered by a visible, verifiable milestone means that if the relationship fails, you are never more than one stage exposed.
- Deposit on mobilisation (materials & setup)10%
- Foundations complete and inspected20%
- Structure and roof watertight25%
- First fix M&E and plastering complete20%
- Second fix and kitchen installed20%
- Retention released after defects period5%
Controlling variations
Variations are normal — London houses hide surprises. What isn't normal is discovering them on the final invoice. Agree the mechanism before work starts.
- Agree a rate card up front: day rates per trade, materials mark-up (10–15% is fair), and prelims impact.
- Require every variation in writing with a price and a programme effect before it's carried out.
- Keep a shared running variations log both parties sign off weekly.
- Hold a fortnightly 30-minute site meeting with written minutes — it prevents most disputes outright.
- Photograph work before it's covered up: drainage, insulation, membranes, steel connections.
- Saying 'just do it and let me know' — that sentence has cost London homeowners millions.
- Paying cash to save VAT. It voids your contractual position and any insurance-backed warranty.
- Letting payments drift ahead of progress because the builder is 'waiting on materials'.
- Allowing the builder to hold your building control certificate hostage against a disputed payment — agree the release condition in the contract.
- Signing off practical completion before the snag list is written and agreed.
When it goes wrong
- 1
Write it down, immediately
Day 1Email a factual summary: what was agreed, what has happened, what you want done. Calm and dated. This becomes your evidence base and, more often than not, it resolves the issue on its own.
- 2
Use the contract's process
Days 2–14JCT contracts contain notice and remedy provisions. Follow them precisely — a valid notice preserves every later right. Withhold only what the contract permits you to withhold, and say why in writing.
- 3
Independent inspection
Week 2–4A chartered building surveyor's report (£600–£1,500 in London) turns 'I think it's wrong' into a defensible technical position. Instruct it before works are covered up.
- 4
Mediation or adjudication
Weeks 4–10Cheaper, faster and far less destructive than court. Many JCT forms name a route; the RICS and CIArb both run consumer-suitable schemes.
- 5
Small claims or county court
Last resortUnder £10,000 goes through small claims without needing a solicitor. Above that, legal costs escalate quickly — which is exactly why the deposit cap, the stage payments and the retention matter so much at the start.
Frequently asked
+Is a fixed-price contract better than cost-plus?
For a defined extension with full drawings, fixed price transfers risk to the builder and is nearly always right for homeowners. Cost-plus only makes sense on genuinely open-ended refurbishment where the scope can't be described — and then only with an agreed cap and open-book invoicing.
+How much deposit is reasonable?
10–15% of the contract sum, and only to cover mobilisation and materials procurement. Anything above 20% before work starts should be justified with supplier invoices. Never pay a deposit before the contract is signed.
+Do I need an architect to administer the contract?
On projects above roughly £150,000 it's worth the 3–6% fee. They value the work at each stage, issue certificates and handle variations — meaning payment decisions aren't a conversation between you and someone standing in your kitchen.
+What insurance do I need as the homeowner?
Tell your buildings insurer about the works — most policies restrict or void cover during structural work. You may need a specialist renovation policy, plus non-negligence cover (JCT 6.5.1) where party wall risk exists.
+What if the builder goes bust mid-project?
Your protection is that you owe them money, not the other way round. That's the whole logic of paying in arrears against completed stages, holding retention, and keeping a photographic record — you can retender the remaining scope from a defensible position.