I know it sounds elementary, but make sure your builder/team come rated. Good building contractors should be able to show you good previous work, and you should be able to speak to a happy client somewhere in London (or beyond).
Yes, you need to know, should your roof fall down that your building contractor has the relevant cover for your own safety and the safety of your home during the renovation.
Your building contractor should feel confident to speak about previous work and happy to supply references of previous home renovations. See how well you get on with them, after all, they may well be in your most personal space for the next few weeks/months.
Is your building contractor all too eager to throw out ballpark figures before he/she has even bothered to see your property? Even for an experienced builder, every job is specific, and they should be pricing you on the specification of your job, not a catch-all quote based on your London location.
Make sure your building team can provide paperwork. Contracts and schedules should be agreed before a single hammer is lifted. A large home renovation is quite possibly the biggest single investment you’ll make in a few years, so don’t let those grubby overalls allow you to fall into a situation you could regret. A contract should protect both of your interests and schedule agreements minimise the possibility of future conflicts.
Make sure you withhold a portion of the proposed budget, and agree a scheduled release of funds at key milestones during the project, with a proportion withheld for completion. Don’t accept a job from anyone who wants everything upfront!
Often, you’ll get a gut feeling about the integrity and capability of a renovation team or building contractors. Follow that intuition, especially when it relates to how you feel about a person. Picking good building contractors should be a positive experience that leaves you feeling optimistic and excited, not apprehensive. If he/she gives you the heeby jeebies, dump them before the project starts! You’ll find someone else to really fulfil your expectations!