Development
A practical checklist for developers choosing a main contractor in London: track record, finances, programme, site management, quality, safety and contract terms.
Lukasz Kisiel MCIOB, Chartered Construction Professional
26 October 2026
Choosing a main contractor is one of the biggest decisions a developer makes. The contractor turns an appraisal into real homes, and most of the risk to cost, programme and quality sits with how well they run the site. In London, where sites are tight, neighbours are close and margins are thin, the gap between a good contractor and an average one shows up quickly.
This guide sets out what to check before you appoint, and the questions worth asking at tender interview.
The main contractor (sometimes called the principal contractor) takes responsibility for building the scheme. They manage the site, programme the work, appoint and co-ordinate subcontractors, control health and safety, and hand over a completed building with the certificates and documents needed for sale or letting.
On a traditional contract the design comes from your team and the contractor builds it. On design and build, the contractor also takes on design responsibility. Our guide to construction procurement methods explains the differences.
Look for completed schemes of a similar size and type to yours. A contractor who builds a 40-storey tower is not automatically right for nine flats on a back-land plot, and the reverse is just as true.
Contractor insolvency is one of the most damaging things that can happen to a development. Check filed accounts at Companies House, look at turnover against the size of your contract, and ask how the business is funded. A contract worth a large share of a contractor’s annual turnover is a risk for both sides.
Consider asking for a performance bond or parent company guarantee on larger contracts, and make sure your payment terms are fair. Contractors who are paid promptly are more likely to pay their supply chain promptly.
The shortest programme at tender is not always the best one. Ask the contractor to walk you through the critical path, the long-lead items, and how they have allowed for utilities, party wall matters and discharge of pre-commencement planning conditions. A credible programme shows they have thought about your site, not just copied the last one.
London sites bring their own challenges: restricted access, limited storage, delivery windows, traffic management, and neighbours who are often only a wall away. Ask who will run your site day to day, how long they have been with the business, and how many other sites they are covering.
Membership of the Considerate Constructors Scheme, and a clear plan for neighbour communication, are good signs.
Ask how the contractor inspects work before it is covered up, how snagging is managed, and what their warranty and building control process looks like. New homes usually need a structural warranty for buyers and lenders, so confirm early that the contractor is acceptable to your chosen warranty provider.
Request the contractor’s accident and incident statistics, any enforcement notices, and their construction phase plan for a recent project. A contractor with weak safety management will also tend to have weak control of quality and programme.
Most main contractors subcontract a large share of the work. Find out which trades they deliver directly, how long they have worked with key subcontractors, and how they manage price rises. Contractors with in-house teams for critical early packages, such as piling, groundworks or frame, often have more control over the programme at the riskiest stage of the build.
Most residential schemes use a JCT contract. Whatever the form, make sure you understand:
A short call with an employer’s agent or quantity surveyor before signing is money well spent.
The right main contractor is the one whose experience matches your scheme, who is open about risk at tender stage, and who has the financial strength to see the job through. Take time over the selection. It is far cheaper than changing contractor halfway through a build.
Kisiel Group works as main contractor on residential schemes across London and the Home Counties, with an in-house piling team for foundations.
Tell us about it. You will speak to the people who make the decisions.
