I second all the warnings about big companies - they subcontract staff and vary rarely have good relationships or even meet the peoe working on your property!!
I'm in the trade and I see too many families left distraught after they've had bodge builders, we are forever cleaning up their shoddy work and it's heartbreaking to watch what the families go through. And shocking to see what the builders leave behind the nicely painted walls that you can't see!!!
Please please please be so careful about who you choose, go with a company who has a long standing history of recommendations from people you know or can talk to for references.
I'm a female electrician so I know lots of brilliant trustworthy tradespeople and contractors, if you need any recommendations just get in touch xx www.female-electrician-London.co.uk