I would highly recommend My london extensions.
We have already talked about them in another post and they have done jobs for many other mummies from this website. They have done our side return extensions but also a complete renovation of one of our other flat and they were absolutely brilliant. Beautiful finishings and very competitive. And also always available to assist you, which we loved.
Their website is
www.mylondonextensions.com and you can talk to David an adorable Frenchman